I assume that minus is an equal sign.

As in the name, marginal, you sum across.

So you have 1/4 probability on these 4 points (0,0), (1,1),(1,-1),(2,0)

P(X=0)=1/4 since X is zero only once at (0,0)

P(X=1)=1/2 since X is one twice at (1,1),(1,-1)

Likewise

P(X=2)=1/4 since X is two only once at (2,0).

OK, now you do Y.