This is pretty straightforward actually, let’s dive right into it. Basically, an FTP allows you to transfer files to your server or web server without actually logging into your WordPress WP-Admin.
So you might be wondering on why use FTP instead of going in WP Admin, take a guess… No guess? Okay, so most of the time we use FTP to either
1- Transfer big files
2- Debug something
In most cases you fall under #2, because if something goes wrong on the backend the chances of you being able to log in to the backend is slim.
Specially, if say there’s bad plugin update and it has a critical error. If it has critical error then your online choice is to delete or temporarily change the plugins folder name via FTP.
Though you could also manage server files through your host provider but with FTP you can ask someone else to do it for you.
There you go, the more knowledge in your brain.