I am still very new to how linux files work, especially how things run and install.
I found caja extensions I want on github but I have no idea how I would install them or which files I should download. Can someone help me understand this?
This is already installed by default so you don't not need to install it. If you want to check run sudo apt install caja-open-terminal for example in terminal to see. To install extra software on your system use Software Boutique. Caja extension exists in official repository so you don't need to use github.