Changing font of mail page

I’m aware that some people like massively bold descriptions but I want to use a different font (maybe 2) where an incredibly bold font announces the title of the directory. I haven’t looked yet at how this theme handles stuff, having only loaded it on my localhost a few hours ago. Ive watched the video but it doesn’t go into much technical detail about this sort of issue.

I would appreciate help here to avoid me stumbling around and getting my word so far wrecked.
My level of expertise with WordPress is not good. This being my first (successful) WordPress directory but I can write PHP as if it were a letter.

Thanks in advance.