Structuring of an embedded web interface

I am trying to improve an existing web UI for a server OS and also learn Javascript by creating a new one using React. I have the website design itself complete, using dummy data for utilisation graphs and users, but I need some help working on the API.

Looking at REST concepts such as HTTP verbs doesn't seem to apply; if I click add user to make a POST request, it's not creating a new user on a database, it's actually creating a new user account within the OS. It seems to me like I just need to make an API with GET and PUT requests, and then a server application for actually implementing the requests to communicate with the web app.

My past experience is mainly with embedded systems so I have no idea what best practices are for this situation. Is this a sensible approach?

Thanks in advance for any advice!