Troop and supply carriers:
You can select troops, GV supplies, or base supplies from the hangar, just like you can select bombs or gun packages for a plane. You should check your options / controls / map keys to see what your "Doors Open/Close" command is. I have the letter "O" set to open/close. You have to be stopped to drop troops and base supplies, but you can be slowly rolling to drop GV supplies. Use your Global / Fire Secondary key to drop the supply box or troops.
Supplies:
The big box of base supplies will re-supply a strat, field, or town to bring objects that are currently down (like auto guns, radar, ammo bunkers, town buildings) and take 10 minutes off their downtime for every box you drop. The small box of GV supplies will allow a player with a damaged vehicle to repair his ride and get back to GV'ing. The "Load Supplies" button will show up for everyone within 800 yards of your supply drop, and they can select the button with their mouse pointer and left mouse button. I have my screen set up so that the "Load Supplies" button appears in the upper left corner whenever supplies are out. Also, the boxes of GV supplies have a limited life of 15 minutes. After that they disappear. Use them or lose them.
Buildings and Structures:
A little complicated, but you have sources of info on what you can bomb/strafe. If it's on a base clipboard map and it's labeled, you can kill the structure. If it's on a strat clipboard map and it's outlined, you can kill the structure. Any structure in a town can be killed. Non of the structures outside of the bases, towns, or strats are destructible. Bridges cannot ("currently"

) be destroyed.
Random, basic tanking thoughts:
1. Tanks have hard areas and softer areas on their surfaces. Sides and rears are softer. Tops of the turrets are even softer. I have seen a P-47 kill a tank in 4 passes by strafing the top of the turret from a near-vertical approach.
2. If you have HE rounds in your load-out, you can track a tank by firing an HE round into the ground right next to the tread.
3. The T-34/85 has fastest turret slew rate in the game.
4. Fire a few times from a position of cover, and then relocate. Fire and maneuver.
5. Sound is your friend. Shut your engine off to help yourself locate other tanks. If you're rolling towards a town, base, or spawn, stop and cut your engine frequently (every 45-60 sec) to listen for enemy vehicles.
6. In the AH3 environment, you should be looking for tank treads below the branch-line of the trees, or the tops of turrets at the bushes or along ridge lines.
7. You don't need to get closer than 1800 yards to kill another vehicle, but you'll probably have to get closer to find them.
8. HE rounds kill guns pits and structures quicker than AP rounds will. Gun pit = 1 HE round, town building = 2 rounds, bunker/radar = 2 rounds, hangars = about 21 rounds.
9. Use the terrain to your advantage. Be in defilade as much as you can (hidden from your enemy's view by staying below ridge lines as much as possible). And when I say as much as possible, I mean if you have a choice between a 2 mile straight-line path to a target, and a 4 mile "C"-shaped path to a target, take the 4 mile path. In the same way altitude and speed are advantages for fighter planes, terrain features and stealth are advantages for tanks. And don't confuse trees for cover. A well-placed tank round will travel through a tree or bush.
10. Do most of your driving from the tank commander's position. I have my position set so I'm standing up, as if I'm up chest-high in the hatch. And I marked dead-center of my monitor with a black dot from a Sharpie pen, so I don't really need to jump to the gunner's position to take a shot. I'll go to gunner for long-range stuff, but for the most part, most of my tanking is done from the commander's position, standing up and out of the hatch.
Other folks will weigh in, but that's what I can think of right now.