I need a basic idea of how bbs are propelled from an Automatic Electric Gun can someone help me.

When the trigger is pulled on an AEG set in the full-auto selector position, a high speed, high-torque motor starts to drive a set of gears, that retracts a piston inside a cylinder against the tension of a spring. When the piston has reached it's full rearward position, it is released by a toothless portion of the main gear, and flys forward. As the piston moves forward, the air in front of the piston is compresed and then released through a tube at the front of the cylinder directly behind the bb at the top of the magazine loading plate. This pressurized air then propels the bb out the barrell, as the motor passes the toothless portion of the main gear and begins retracting the cylinder again, repeating the process.
The feed mechanism of an AEG is generally one of two types. There is a simple spring magazine that uses a coil spring to drive a single column of bb's toward the top of the magazine, where they are retained by a small spring loaded stop. The other type of magazine is a spring-wound high capacity magazine. It uses a coil spring wound up by a wheel on the baseplate that turns a set of internal gears to drive the bb's up to the top, where they also are retained by a spring-stop. When the magazine is inserted in the gun, the stop is pressed back by the loading plate, and the bb's feed up into the mechanism, where they find themselves one by one with the pressure tube aperture behind them and the barrel in front of them, ready to fly.
Hope this helped.