Is the rhyme scheme "abab" 2 stanzas or 4 stanzas? How do I determine the number of stanzas?
The rhyme scheme "abab" is probably only one stanza or, perhaps, only part of a stanza.
A stanza in poetry is equivalent to (although more structured than) a paragraph in narrative writing. The rhyme scheme is (normally) internal to the stanza.
Here is a sample with the "abab" scheme, repeated in two stanzas. (Apologies, I couldn't think of a poem with this scheme, this is the best I could come up with on short notice).
My Uncle Joe would never smile;
He would always gripe and moan
And complain with bitter bile,
"Why won't you leave me alone?
"I don't need your smiling face
Or cheery voice filling my room.
I don't want you in this place.
I am happy in my gloom."
Note that this might have been written as a single stanza.