Griving any vehicles is pretty simple. E is to start engine, Q is gear up, and W is gear down. push your joystick/mouse foward to move, back to stop, left and right to steer left and right. To gun press the #2 key to switch the main gun on tanks and ostis, and the MG on Jeeps, M3s, and LVTs. #3 key is to switch to pintle gun on tanks and the hull gun on the osti. #4 key will switch you to the hull gun on tanks. Fire all the guns using the primary fire button. In tanks, when you are in the main gun you can use the secondary fire button to fire a co-axial MG.
If you not in the driver postion (key #1) you can still steer the vehicle by twisting you're joystick/mouse like using rudder in a plane.