My first practice of verb to be.

-I'm Andrew. Good
-You're my partner for practice English. You are my partner to practice English with.
-Juan is riding his bike Correct
-Adriana isn't my girlfriend  isn't is informal. Use Adriana is not my girlfriend instead.

-it's hada, my Cat. Correct; Although it sould be "It's" not lowercase i.
-they're from Canadá. Informal, but correct.
-Weren't living in Belarús. This is incorrect. It does not make sense although i see why you would think so. You are safe using the full expression "We are not living in Belarus" and this makes much more sense/ is formal.
-Am I a hispanic? If you are asking a parent or someone if you are hispanic this would use a "?" question mark, but the a is not needed. instead say "Am I Hispanic?"
-Are you an American or British? Again, you do not need the "an" you can simply say, "Are you American or British?"
-Is he a good man? CORRECT
-Is Laura traveling alone? CORRECT
-is it your pet? This is correct in the appropriate context.
-Are they working with a contract? CORRECT
-Are we the champions? CORRECT, although you could also use "Are we champions?" depending on the context of the question.