Ok, to give you a bit of an answer to your questions:
i want to know the difference between a safety and a de-cocker,
Basically, a decocker takes a cocked hammer (gun ready to fire, the trigger only needs to drop the hammer), and gently lowers the hammer.
A safety prevents the trigger from being pulled.
It gets a bit more complicated because some guns have combined safety/decockers. In a combined system, when the decocker is used, the safety is simultaneously engaged.
In guns with separate systems, the gun can often still be fired after using the decocker because the trigger is "double action", which means that it can not only drop the hammer but also cock it.
I'm no expert on these decocker systems, so I might be being overly general here. If so, someone will be happy to clarify shortly.
a reguler mag and a drop free mag,
A "regular" magazine is one that doesn't necessarily fall out of the gun when you push the magazine release button. A "drop free" magazine drops from the gun by gravity and/or spring pressure when you push the button.
and what MOA means. Any info is greatly appreciated
MOA means "minute of angle".
Basically, imagine a clock with 360 sections rather than the normal 60 minutes, then each of those degree sections is further divided into 60 sections. Now, imagine the clock is really, REALLY big and laying on the ground.
The amount of distance covered by each 1/60th of each degree on the clock is a "minute of angle". If this clock had a radius of 100 yards, each minute would cover about 1 inch (technically 1.0471996 inches, but we basically ignore that extra bit).
As you can possibly imagine, as the clock gets bigger and bigger, the amount of space covered by each tick of "minute hand" would cover a larger area. 2 inches at 200 yards, 3 at 300, 10 inches at 1000 yards.
