Fire burn and cauldron bubble

Each puzzle has three categories.

For this tutorial we will use:
Words with A, Words with B, Words with C

Three words belong to only one category.

BEE (has B), CRY (has C), ALL (has A) each go in a different outer region.

Three words belong to exactly two categories.
ACT (A & C), BAT (A & B), CUB (B & C)

One word (CAB) belongs to all three!

Each one goes in one of the inner regions.

Real categories won't be this obvious.
Good luck!