Configure access to the server by FTP

You need to configure access to the server using the FTP protocol. At the moment, there is only access to SSH. The server already has sites and FTP was not required before. But now you need to separate access to some directories for different users, but SSH access does not want to provide. I watched on the Internet how to set up an FTP server and I am afraid that I will spoil something in the work of sites.