As per the title, how can I make my own LEGO instructions?
Use LDD. LDD is a free program made by LEGO that enables you to build LEGO creations digitally, and it automatically can produce instructions for whatever you build. The main downsides are that it's very hard to use and the selection of pieces is not amazing, and that it is no longer being updated by LEGO. I use this program. Another option is to use stud.io. I don't know very much about it, but what I know is that it's a program made by BrickLink, and you can make your own designs for stuff and buy them off of bricklink.