It sounds like your editor doesn't have the permission to modify the files you are trying to modify or create. I would review this guide on permissions.
What user are you logging in with the editor with? What error are you getting? Can you give us the permissions of the folder you are trying to modify?
You likely just need to modify the permissions of the public folder so that you can modify and create things while keeping the web able to read them.
It's important to understand that when asking for help to provide as detailed information as you can. We can only help if we can replicate or get enough information to know what's going on :)
Linux is a multi-user OS that is based on the Unix concepts of file ownership and permissions to provide security, at the file system level. If you are planning improving your Linux skills, it is essential that have a decent understanding of how ownership and permissions...