How do I merge two drawings together??

It's difficult to anwser your question - but you can try this:

Just select both shapes (drawing) and choose Shape Builder Tool (Shift+M) then just drag over both shapes to merge tchem into one object

Or can you show us an inspiration image like what you're hoping to create? Is it something like a double exposure effect with a blend mode?

A screen shot would be helpful here, otherwise we are guessing at what your issue is.

There are multiple things you might mean. It might be that you have a two obects that you want to become one. Maybe they are open, maybe they are closed. Maybe you want to join paths together, maybe you want to merge shapes. There are so many different questions you might be asking.

Can you be more specific? Do you want to copy and paste from one file to another? Can you show us what you are working with to give us a better idea of what you want to do.