Site Fonts

I can’t seem to figure out how to edit the fonts being displayed throughout the site (mostly just concerned about the site title font). I tried to install a plugin that worked just fine on another theme for a different website I have and it gave me warning errors here after I activated it and it wouldn’t work properly. I thought maybe I should try a different plugin and this one gave me a fatal error and said to remove it. Do you have some kind of coding not allowing fonts to be changed or any plugins to alter the fonts for some reason? Has anyone else been able to do otherwise?