What is 12× - 4y I'm having trouble please, Thanks!

Please clarify your question. You wrote:

12x - 4y

This seems to be part of an equation. Please (a) provide the complete problem you have been given, and (b) show us what work you have done to try to solve it yourself.

You cannot combine any terms in where because it does not have any like terms--variable(s) that are raised to the same power.

Since the question is vague, I can only assume that you can simplify the expression 12x - 4y by factoring. The common factor of both of these terms is 4, so you can do:
4(3x - y)

You can check whether this factoring was correct by using the distributive property.