'A' lets you enter combat, 'F1' lets you see the controls. If you need an in depth guide here. But well you know, spoilers. I recommend saving often enough and on 3 separate slots. If combat really is too hard you can change it in the options, there is also the always run option that makes running the default and holding shift makes you walk instead of run which is the default.
I love Fallout 1 & 2 but they have problems. One of which is how there really are bad ways to build your character that can result in you being screwed over. There are rubbish skills like Throwing and skills that are useful but not until way after you start like Energy Weapons. If you're willing to start again my recommended build for Fallout 1 and 2 is:
S: 5
P: 6
E: 5
C: 7
I: 10
A: 10
L: 4
Tag: Small Guns, Lockpick, Speech
Traits: Gifted, Good Natured.
Some recommended perks for Fallout 1: Awareness, Bonus Move, Bonus Rate of Fire, Tag (to take Energy Weapons later on)
Be careful what you say. Say the wrong thing, [&@%!] someone off and they likely won't want to work with you, may even want to kill you. Aimed shots can be good but only the Eyes and the Head are worthwhile. Don't kill children or everyone in the world will hate you for pretty understandable reasons.
Leave Vault 13 for one day and when you return you can do some quests. Use a computer on level 3 for some XP, talk to the overseer for supplies and you can get into the armory by persuading the guard outside, there's a shotgun inside which will really come in handy early on. Ask in every settlement about the water chip, look out for people who would know about vaults and about water they should point you in the right direction. The game doesn't end once you get the chip but after you take it back there's no more time limit. You can extend the time limit by paying some water merchants in one of the cities
2 Rad-X will give you 24 hours of full radiation immunity. Assuming you don't sleep or waste time and take it as soon as you need it you should have enough time in irradiated places with just that. You'll need three rope in the entire game, two for Vault 15 and one for The Glow.
There is a guy south of Bob's Iguana Bits in the Hub, if you do a mission for him (have to be level 5 first) you can get the best Small Gun in the game. It's the .223 Pistol, "That Gun" from Fallout: New Vegas.
Wait until after you get the water chip back to try to join the Brotherhood assuming you want to. Their quest will take a long time and you don't want to spend that long while you're still on the clock. Joining really is worth it.
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If you are really, really stuck about the Water Chip I'll put it in this spoiler but don't read it unless you really need it.
Spoiler:
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The Temple of Trials at the start of Fallout 2 sucks. It's awful, one of the worst tutorials I've seen. Also you basically need to have tagged Steal, Speech or Unarmed to beat it.
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I'm playing Fallout: Tactics at the moments. It's very meh, play it if you want but you wouldn't miss out on much if you skipped it. It is sort of canon though, not fully, it has a lot of inconsistencies. One of the scribes in Fallout 3 mentioned the Brotherhood in Chicago.
