Full Face Scuba Mask Scuba Gear?

Scuba Gear? - full face scuba mask

Hello

I started diving courses and have questions
First, what it is to use a respirator and breathing apparatus
What is the difference between a respirator and a face mask, how it feels with a full face mask, as some have said strange shots and have problems with it, and finally I have a T-shirt in the pool for BCD in places others have recommended

THX