Controlling font type and size

I’m using the My Music Band theme for My Guitar Riffs website; at https://www.myguitarriffs.com. I will be creating diagrams with supporting verbiage and would like to know how to control my font type and font size of all the content I’m creating. Please let me know where in the theme I can get this accomplished. Thank you…

The page I need help with: [log in to see the link]