Welcome to knitting!!!
Please don't be frustrated. You are, where we all were, once.
First, congrats on making some garter stitch squares.
Second, you are very brave to go from small squares to mittens. That would likely not be most peopel's first real project, and is probably why you feel so frustrated. While very basic mittens could be doable for some new knitters, getting a good fit requires understanding sizing/fit, needle sizes, yarn substitutions, gauge....