I made 2 custom hat mods but I can't get my textures to appear in the game. Are there any specific pixel art programs or image sizes that I have to use? I'm new to modding so I don't know ANYTHING yet.
No there are no specific programs, although I'd avoid regular MS Paint because it doesn't support transparencies. Your problem is more likely you doing something like misspelling the asset name, messing up the .frames file, etc. Your log should tell you what is really wrong.
I used ms paint to create a simple sprite for a hat and I actually got it to become transparent but it still wouldn't work. The file names are correct but I have no idea if one of them requires a specific image layout (like a spritesheet for example) or how the mask file works and what it does.