I suggest you deploy to the warpgate asap . Open map and check on the list of deployable places for one with the "warpgate" word in it. This is the main base. I have no idea why SOE didn't let everyone start there, because it's rather dumb to throw newbies right into the middle of a warzone. At the warpgate you can check out all the vehicles and classes and change continents (there are 3). So if you don't like the desert scenery, there's a more forest continent.
As for taking shots, there's a TON of upgrading to be done in terms of health, shields and defense against various type of damage. Heavy Assault gets by default a special ability shield to protect against a few more hits, where the default class "Light Assault" gets a jetpack instead . The 5th "class" which is more like a vehicle is a MAX , that is kinda like those Starcraft Terran dudes who climbs into a suit, anyway a MAX is very scary , you will not take one down very easily . Catch with a MAX is, it costs resources to be one, so just like vehicles you can't just respawn in a MAX everytime, there will be a cooldown etc. MAXes also need engineers to repair them, not medics.
Also the figuring out who to shoot thing? From beta, rule of thumb, if the enemy does NOT have anything above their heads, SHOOT. By pressing "Q" you can spot an enemy (same as Battlefield), if you spot an enemy it will put a red tag above their heads and show them on the map. If other people spot them for you, you will also see the red tag. So if i'm scanning the horizon for enemies i tend to sweep by pressing "q" to highlight enemies. Either way, if you haven't spotted them, they will have no markings above their heads and you can assume they are enemies.
All allies will always have a blue (same faction) or green (same squad) marking above their heads. Anything that is not blue or green you shoot.