Every race has their own set of skills and weaknesses, as well as their own sets of stereotypes that other people see in them. Your race will affect your skills and the reactions of others.
Council Races
Human - Humans are the versatile inhabitants of Earth, with the potential to excel in any field they partake in. Gaining vast notoriety in the galaxy for helping to save the Citadel Counil during Saren's assault on the Citadel, and later during the war against the Reapers, the humans have bested the animosity their race had faced and now sees unprecedented acceptance in the galaxy. Humans get +1 in any two CASPIE attributes (Up to a maximum score of 10) of their choice.
Turian - Turians are the steadfast, strict people of the planet Palaven, who make excellent soldiers and officers. They are respected for their public service ethic—it was the turians who first proposed creating Citadel-Security—but are sometimes seen as imperialist or rigid by other races. Turians get +2 in Perception and +1 in Endurance, but a -1 in Agility (to a maximum score of 10 and a minimum of 1). Turians are
Dextro-Amino Acid beings, and cannot eat food or use many ingestible products designed for Levo-Amino Acid beings (beings that include everyone but Quarians).
Asari - Asari are often considered the most influential and respected sentient species in the galaxy, and are known for their elegance, diplomacy, and biotic aptitude. A mono-gender race, the asari are distinctly feminine in appearance and possess maternal instincts. Their unique physiology includes the ability to reproduce with a partner of any gender or species to produce Asari offspring. Asari get +2 in charisma and +1 in Endurance, but a -1 in strength.
Salarians - Salarians are known for their observational capability and non-linear thinking. This manifests as an aptitude for research and espionage. They possess a hyperactive metabolism; they think fast, talk fast, and move fast. To salarians, other species seem sluggish and dull-witted, especially the elcor. Unfortunately, their metabolic speed leaves them with a relatively short lifespan; salarians over the age of 40 are a rarity. Salarians get a +2 in Intelligence and +2 in Agility, but a -1 in Strength and a -1 in Endurance.
Non-Council Races
Krogan - The Krogan are the recovering natives of the planet Tuchanka. Previously afflicted with the Genophage virus for their role in the Krogan rebellions, the krogan were dwindling in the face of minimal fertility rates. After the curing of the genophage, Krogan have returned to high birth rates, and have defied expectations by showing themselves to be a civilized people instead of returning to their militant, barbaric past. Still, they are mistrusted in CItadel space for their past atrocities. Every Krogan gets a +2 in Strength and a +3 in Endurance, but a -2 in Agility and a -2 in Charisma.
Drell - The client race of the Jellyfish-Like Hanar, who all live in climate-controlled domes that simulate the arid environments of their old home planet. Drell are naturally agile and excel as covert operators. Having recently been introduced to a cure for the rampant Drell disease known as Kepral's syndrome, Drell are experiencing a period of newfound hope and confidence in their species' future. Drell get +2 in Agility and +1 in Endurance, but a -2 in Strength and suffer from extremely precise memory relapses, which can be triggered from any number of outside stimulus and results in a Drell muttering a description of the event while it flashes before their eyes.
Quarians - Quarians are a previously nomadic species of humanoid aliens known for their skills with technology and synthetic intelligence. They have recently left behind their nomadic nature after reclaiming their homeworld and coming to share it with the Geth. They typically remain outside of Council Space, but still send coming-of-age adults on Pilgrimage to return to their communities with something of use. Quarians get +2 in Intelligence and +1 in Perception, but get a -1 in charisma and -1 in endurance. Quarians live in environmental suits, and when a rupture occurs, a repair must be made using the mechanics skill or damage will continue to occur even with medi-gel being applied and healing being done. Quarians are
Dextro-Amino Acid beings, and cannot eat food or use many ingestible products designed for Levo-Amino Acid beings (beings that include everyone but Turians).
Batarians - A disreputable species that chose to isolate itself from the rest of the galaxy. The Terminus Systems are infested with batarian pirate gangs and slaving rings, fueling the stereotype of the batarian thug. It should be noted that these criminals do not represent average citizens, who were previously forbidden to leave batarian space by their ubiquitous and paranoid government before the Reaper war. Many batarian worlds were scorched beyond habitation by the Reapers, thus they are seen on a number of Council-space planets and beyond looking to return to a normal way of life. Batarians get a +2 in strength and a +2 in Perception, but a -2 in Charisma and a -1 in agility.
Vorcha - The vorcha originate from Heshtok, a small, hostile, overcrowded planet which has been largely stripped of natural resources by successive generations of this fast-breeding, savage species. The lack of resources has resulted in a tight-knit, clan-based society in which rival clans wage constant war against one another for control of scarce resources. Even as their population grows, the vorcha constantly fight each other in fierce competition over basic necessities. This incessant warfare has made each generation of vorcha stronger and more aggressive than that which preceded it, but their continual lack of resources has kept vorcha society extremely primitive. Vorcha get a +2 to Endurance and a +2 in strength, but a -3 in Charisma.
Geth - The Geth are a race of networked AI platforms that have recently reached sentience after their newfound peace with their creators, the Quarians. Having been the 'boogeymen' of cautionary tales for over 300 years, coupled with many renegade 'heretic' geth siding with Saren and the Reapers, the Geth are still subject to much distrust and are rarely seen outside of Quarian space. The Geth get a +4 to Intelligence, but a -3 to Charisma.
You can also play as a hanar, elcor, or volus, but be warned; they will be difficult to play, and I warn you to not play one unless you're quite an experienced roleplayer and aren't afraid of dying in combat rather quickly if it comes to such.
Hanar - The hanar are a species resembling Earth's jellyfish and are one of the few non-bipedal Citadel races. Hanar are known for their intense politeness when speaking, and their strong religious beliefs regarding the Protheans, whom they refer to as "the Enkindlers". As a hanar, you will not be able to hold any conventional firearms (without use of biotics), and you will be restricted to the adept, engineer, and sentinel classes. A hanar receives +2 in intelligence and a +2 in charisma, but a -1 in Endurance and a -2 in strength.
Elcor - The elcor are a Citadel species native to the high-gravity world Dekuuna. They are massive creatures, standing on four muscular legs for increased stability. Elcor move slowly, an evolved response to an environment where a fall can be lethal. Their speech is very monotonous and they use adjectives to indicate the tone of their sentences. As an Elcor, you will be restricted to shoulder mounted weapons, and your huge size may cause complications. An elcor gets +3 in strength and +3 in Endurance, but a -4 in agility and a -1 in charisma. Elcor cannot be infiltrators..
Volus - The volus are an associate race on the Citadel with their own embassy, but are also a client race of the turians. They hail from Irune, which possesses a high-pressure greenhouse atmosphere able to support an ammonia-based biochemistry. As a result, the volus must wear pressure suits and breathers when dealing with other species. Because they are not physically adept compared to most species, volus mostly make their influence felt through trade and commerce, and they have a long history on the Citadel. A Volus receives +3 in intelligence but a -1 in strength and a -1 in agility. As a Volus, you will run at a much slower pace than most races due to your stout stature, are your limited arm length restricts you to single handed weapons like pistols and submachine guns. Volus cannot be soldiers.