Quitting my first job!

I don’t know if this is the right group to post this on but here we go:

I got a part time job 6 months ago and I’ve never been happy with it. My last shift ended with me almost crying and having to leave early bc of how stressed I was. I decided I need to quit but I have absolutely no idea how to do it. I just feel bad because it’s in the middle of holiday season.

This is my first job, I’m just so nervous. My next shift is tomorrow! Do you guys have any advice or stories? An outline of what I should say to my boss? Please, anything will help me!