If you right click on the left side of the screen in the gray area, a menu will pop up. The instructor wants me to make a new folder, we are making external links. However, I get this error-"An error occurred after trying to create the directory css.(Error Unknown) At first I thought it might be the actual name of the directory but it isn't, I tested it with my own name. Any help would be appreciated, thank you very much in advance.
It looks like your current opened project/directory in Brackets is the default Getting Started project. This means that whenever you create a new file or directory in the sidebar, Brackets is trying to create a file or directory in that demo project, which likely fails because it does not have permission to write there.
To fix this, simply open a directory where you have permission to write to.