Please elaborate on what you don't understand.
To summarize, you have to upload the wanted font file on your wiki. If the file type is not allowed on your wiki (see Special:Upload on your wiki), contact Fandom to allow it.
Once uploaded, you have to call the font in your CSS — with @font-face and the URL of your file (that's the "Original File" link, seen on any media page.)
Once called, you have to assign the font to a certain element of your wiki. (For help about this step, please open a new topic with a link to your wiki.)
