I just figured it out, this probably should have been intuitive but for anyone one wondering, you need to add cubes on the right hand side and make a model of the correct shape first to then apply the texture to.
I have only made one texture pack, It was kinda for myself because I wanted to make scaffolding look better, but decided to share it since I had made it anyway. It has almost 800 views, but considering I didn't put a ton of time into (besides figuring out how to make it) I'd consider that pretty successful lol