Is there a guide that explains the different types of multiplayer matches that I can take part in? Also, is there a list of the different unlocks that I can get for the various classes that I play on my Battlefield 3 account?
Finally, could someone please explain to me the HUD in detail to me (both for ground combat and for when you're inside of vehicles)?
This is kind of hard to answer because it's not exactly clear what the question is. There are two primary game modes in Battlefield 3.
Conquest
Capture and hold points A-E. To capture stand near a point. The more people standing near the point, the faster it captures or uncaptures. The more points you hold, the faster the opposing team's lives go down over time. When one of the team's lives gets to zero, they lose.
Rush
One team plants a bomb on objectives A and B, the other team tries to prevent/defuse. Game is over when the attacking team runs out of lives (displayed in the lower left) or all the objectives are destroyed.
There's also deathmatch and team deathmatch, everyone hopefully knows what those are by now...
In general, this is my advice to new Battlefield 3 players:
Spot everything, all the time. The spot key (or button; it's q on PC, back on Xbox, and select on PS3) lets everyone else on your team know where the bad guys and vehicles are. Spot spot spot spot! If you do nothing else for your team, please spot baddies! Always! This should be instinctive.
Don't ever go anywhere alone. Buddy up. Find your squadmates (in green) and follow them around. If you are not in a squad, join one using the SQUAD tab on your loadout screen. If your squad is filled with idiots, leave the squad and find another. Try to pick squads with players of higher rank so they aren't beginners and at least in theory know what they are doing.
Always spawn on your squadmates when possible. Choose your spawn point via the DEPLOY tab on your loadout screen, which will include each of your squadmates, provided they are still alive. If you cannot spawn on your squadmates, spawn at a nearby point -- perhaps not too close, if you are getting killed a lot, to give you time to approach the action without appearing in the middle of it.
Move from cover to cover. Don't just run down the middle of a field or street. Pick one piece of cover, then pick a path to the next piece of cover toward your objective. Repeat until you arrive.
Play the objective. Those big visible A-E letters are what everyone is fighting over. Just shooting bad guys is not enough. If you want to win, help your team achieve the objectives of the map.
Half of the battle is knowing the map. It helps a lot to know the common entry and exit points on the map, because otherwise it feels random -- like anyone can be coming from anywhere! Try to stick to one map for a bit and learn it reasonably well, before moving on to the next "never seen this before, no idea where anyone is going" map.
Use a microphone. Talking to your teammates is very helpful. Try and get in a squad where others are talking, and talk to them. This is a great way to improve your game - you'll become more aware, work better together, and maybe even pick up tips from more experienced players.
Of course there is tons more, but that's the essentials.
To add to Jeff's answer: Be useful...
If you are a medic, be liberal with handing out medikits. Whenever you dash and stop, leave a medikit. See a team mate, drop a medikit.
Same with support: leave plenty of ammo boxes. For some of the urban maps, grenades become very useful so your team mates will like you when you replenish them.
Don't run around aimlessly. If in doubt, find cover and look about for baddies and try to spot them. If you run around 'looking for action' then you WILL get shot. Or knifed. Or RPG'd!
If your team arm the MCOM, then don't just stand there looking at it! Turn around and look out for the defenders coming to disarm it. If your team mate looks left, then look right and cover his six. Scan the rooflines. Spot spot and spot.
If you have a headset (when it works) then don't speak drivel and yammer on and on.
If you get into a tank or vehicle as the second passenger then use the machine gun to spot, to kill engineers and recon's with a handful C4 running up to toast you. Don't look forwards (the same way the driver is driving) but look-out to the left and right and behind and up (where the driver can't see) and take out infantry, choppers, jets etc.
Oh, and remember to blink! Your eye's can get very dry and sore after a couple of good games!
If you're willing to pay a few extra dollars ($10 at Best Buy, $12.50 at Amazon), the Battlefield 3 Official Game Guide from Prima is impressive. You could shell out way more for the hardcover Limited Edition version, but I don't recommend that.
The first 20-ish pages are a primer with a quick but surprisingly thorough overview of basic game concepts. Then it goes into tons of detail for any class, vehicle, map, or game time you'd like to learn more about.
If you're not up for the extra dollars, I don't know of a great online overview yet. Often major gaming sites will put together game guides or walk-throughs, but usually not this early. IGN has a really pretty good start to a guide which may get better over time. I don't see coverage of some really basic stuff like the elements of the HUD, but you can get that from the official guide (which is has pretty limited value otherwise).
For most games wikia.com in an excellent resource. It's usually most helpful when you want to answer a specific question than when you're looking for an overview. The Battlefield 3 Wikia site is coming together.
