Ferdi, as opposed to Franz, allows you to use a custom server to save your account data. As a normal Ferdi user, you'll probably never have to deal with changing or setting up a server.
To use the default Ferdi server, simply input
https://api.getferdi.com into the server setting (it should already be set to that by default), and you can use Ferdi like any other app. Additionally, you can use the "Use Ferdi without an Account" option to simply store your data on your own computer instead of a server.
If you are however very privacy concious, you are in the IT department of a company or your anre simply interested in it, you can set up your own Ferdi server to store your account data. Look at our Guide to setting up a server for more information.