So i am part of a play group who just got into the game this year and I am dming my first game. What I need help with is how to mix different cultures. What do elves and dwarves eat? What kind of music do dragonborn and goblins listen to? Is there a resource book for it? Help please lol

Generally, if you're having trouble coming up with a starting point, the first place I like to start looking for this kind of stuff is Geography, specifically climate zones. Look into how hot, cold, moist and dry a particular environment is, and then ask yourself what real life cultures living in environments like that ate, what sorts of traditions they developed, etc. Basically, you're taking historic Earth cultures and using them as a cheat sheet. Once you have a baseline, use magic and any prevalent racial traits to introduce new spins on your borrowed "real" culture, until it becomes distinctly its own.

So let's say you're making a Dwarven culture. My question to you would be, where do your dwarves come from? The default answer tends to be deep inside of or around icy mountains, but from whence do these mountains come? Perhaps they're surrounded by a lush jungle like the Inca? Or do they live up north, having more in common with the more default depiction of Nordic tribes?

Already this gives me a fun idea - Incan dwarves. I'm not sure how well it'd work out, maybe a different race would suit better for such a task, but the point is that geography is generally one of the best starting points for building out a culture, because so much is determined by it.