SilentLizard,
I would be more than happy to answer the latter questions, as long as you're prepared for a short-story-length read!
Main Weapons (Sub-machine guns, Rifles, Shotguns, Machine Guns.):
/////RIFLES
Alright, first things first -- your most powerful weapon is going to be one of two things, depending on the team you're on:
Terrorist - AK47,
Counter-terrorist - M4A1.
These are the weapons you should buy most often! They are cheap and versatile, fitting almost any situation (with practice).
The first thing you're going to want to do is get a feel for each weapon's spray (the pattern in which the gun shoots when the trigger -- mouse button , or whatever you set it to -- is held down; this coins the phrase spray and pray, meaning you are holding the button down praying that the 30 bullets you are spraying hit and kill something).
I would include screenshots, but my description will do just fine, I think --
The spray for almost all the weapons in CS:S is "T."
Literally, the spray looks exactly like the letter T. You start at the base of the letter, shoot upward, then move left-to-right (or right-to-left).
With the AK, the spray is dominantly on the left portion of the T; hence, when you spray (at about 50-100 metres), you should aim down and to the right of your target.
The M4A1's spray is a bit more unpredictable, but I've noticed that it will occasionally make a "7." Again, you want to aim down and to the right of your target.
Important note: In Counter-strike, contrary to Battlefield, spraying is highly inaccurate and is not at all suggested unless absolutely needed.
The best strategy is to pull off shots in 3-5 round bursts. This in mind, do NOT aim for the head unless in CQB (Close-quarters battles). You should be aiming around the neck if you plan on shooting more than 1-2 shots. If you are confident in nailing the head on your first or second shot (which is quite easy), then aim -- still -- toward the mouth/nose. Do NOT aim for the forehead because if you, unexpectedly, have to pull off more shots, which kill accuracy, you're going to have to readjust your shot.
It's easy to get excited when shooting, and be prone to spam/spray, but be sure if you start to spray, you stop yourself and start slowing your shots.
Sniper rifles... Well...
The AWP is amazing. One-hit-kills unless you hit them in the foot or hand. There's certain taboo about the gun and I don't suggest using it. The Scout will kill in one-hit if you hit the head and shoots faster, reloads faster, and doesn't get cried over.
Auto-snipes (SSG500, IIRC) are looked down upon, but are the best way to counter a pesky AWPer. They are semi-automatic weapons that have the scope of an AWP. The general rule is 3-hit-torso-kill and 1-hit-headshot.
The Krieg and Bullpup are NOT autosnipes and do NOT have scopes, they only have about a 1.5x zoom. These are great for mid-to-long range maps. These guns are NOT spam material; furthermore, if you absolutely MUST resort to spray, ensure you are not scoped in. Your firing rate drops tremendously.
/////Sub-machine Guns
The TMP and Mac-10 are amazing, but have very short clips. They are generally 2-hit kills (headshots), and are very inaccurate. Only use these in small areas. You'll be putting out a lot of bullets very quickly, so aim for the head anyway.. you'll stay accurate enough in the range you'll be shooting.
The MP5 Navy (MP5) is VERY, VERY accurate when spraying and, in fact, with any SMG, all you CAN do is spray. That's what they're there for. Spray away with these and ignore the rifle rules above. Aim for the head, 'cause you're going to be within a range where deviation won't matter too much.
The UMP is useless, do not buy it.
The P90 is as accurate as the M4A1 within your first four or five shots but has another 20 rounds and a faster firing rate. The problem lies in the bullet deviation, after the first few shots, you're shooting ALL OVER the place. Aim for the center of mass, not the head with this gun. (Collarbone/sternum highly suggested.)
/////Shotguns
The M3 (top shotgun) is far more powerful than the Autoshotty but you suffer a dramatic down-time between shots with the M3. The autoshotty, IMHO, is inferior to the M3.
The M3 can get some pretty ludicrous kills -- 100m headshot kind of thing. Don't be afraid to spam a couple shots off then hide.
You can interrupt shotgun reloading to pull off a shot. Be sure to do this rather than sit through the reload time if you come into contact with a hostile!
/////Machine Guns
The M249 is... pretty much nothing more than a scare tactic. It's good for laying down suppressing fire but for as much as it costs, it really isn't worth it. It has, literally, one accurate shot and that is the first one. (You're gonna be looking at very near to 100% accuracy that first shot with the SAW.)
I do not suggest buying this; but, it's good for a laugh and to scare people.
Note: The P90 has a similar RoF and has a much smaller CoF -- I advise buying that in lieu of the SAW; the only thing you're sacrificing is, IIRC, 150 bullets per clip. The P90's reload time is much, much shorter than the SAW's so it balances out rather well. The SAW has the longest reload time, so you better have a good sidearm or someone willing to cover you while you're reloading!
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Sidearms (Pistols):
These are pretty straightforward and incredibly accurate. The thing to keep in mind is just use common sense; if the map is large, a pistol like the Desert Eagle [Deagle] (which is often a one-hit-kill-headshot) will be far more accurate over distance.
The USP (Counter-terrorist default pistol) is far superior in one-shots to the Glock (Terrorist default pistol). The Glock has a secondary firing mode - Burst-fire. USE IT.
ASSUMING EVERY HIT IS IN THE HEAD....
The USP is GENERALLY a 2-hit-kill.
The Glock is GENERALLY a one-hit-kill on Burst-fire (you are, after all, throwing three bullets instead of one).
The most powerful mid-range pistol is going to be the P228 Compact. I highly recommend it. It often will get one-hit-kills, as long as you hit them in the head.
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Equipment (Grenades, Defusal Kit, Kevlar, NVG):
I'll be the first to tell you.. Night-vision goggles are absolutely useless. Turn up your brightness and you'll never have to spend the money on this item. Don't even THINK about purchasing them unless absolutely necessary (there are some custom maps that are dark enough that you are required to purchase them to see).
As a CT (Counter-terrorist) Defusal Kit is priority! Always buy this! It's $200. If you have to sacrifice a better pistol (the USP is pretty much all-purpose anyway, so it's fine to stick with it) just to get the Defusal Kit, DO IT.
Grenades -- buy a frag and a flashbang when you can. Do NOT prioritize these.
The smoke grenade is good, but only when you have the money to buy it. Again, do not prioritize and sacrifice other items for any grenades.
Kevlar -- Don't buy Kevlar alone, always go Kevlar + Helmet (It's $1000). Since everyone is aiming for your head anyway, having extra body armour is near useless.
Main weapons are ALWAYS the best way to go. Save up. In certain situations (particularly when your team is losing often), it's perfectly okay to buy a pistol for a few rounds so you can afford a rifle on that 3rd round. Just don't waste money on extra things -- buy the pistol and nothing else.
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Teamwork:
Don't expect this, but don't... not expect it either. You'd be surprised how many Pubbers are willing to follow a decent strategy.
Be sure to call out frags and flashbangs before tossing! Your teammates will thank you in the long run.
("Frag out," "Flash, look away!")
From people like me, you can occasionally expect a squad-member-esque role, but... CS:S doesn't require teamwork to win. It's very arcade.
I hope all this helps, buddy!
Biscuit
EDIT: Added M249, fixed some minor grammar issues (I'm certain more exist).