In ACRO, you will have full control over the throttle (that is going to propel the drone upward), pitch, roll and yaw (that are going to rotate the drone on its axes). To move forward, you pitch the drone forward and it will start moving in that direction.

Is air mode same as acro?

If you just had acro mode enabled (by default in most flight controllers) whenever your throttle stick is at zero, manoeuvring the drone while it is in the air is harder than being in air mode. Air mode still keeps the PIDs looping even when the throttle stick is at zero (find out about PIDs here).

What is acro mode in FPV?

Acro mode uses the RC sticks to control the angular velocity of the copter in each axis. Release the sticks and the vehicle will maintain its current attitude and will not return to level (attitude hold). Acro mode is useful for aerobatics such as flips or rolls, or FPV when smooth and fast control is desired.