Gbxcart need help making project

[GBAbegins]

I need help figuring out how to use gbxcart properly I'm a beginner. I'm trying to find reproduction cartridges on AliExpress that will work to flash ROMs. I also don't know what type of ROM hacks I am able to put on there because of the file type. I also do not know how to patch. Ugh I thought this would all be easy but apparently not. I would love a hands on tutorial on all that. I'm working a project I just can't leave behind