For years websites were pretty much limited to using the fonts that visitors had on their computers. You could choose a serif or sans serif or several other options, and if the visitor was using Microsoft Windows, you might specify Arial, Times New Roman, Courier New, Comic Sans, or a few other styles. If they were using a Mac or other operating system, you might get an equivalent, or not.
You could always make an image with any font you like, and put that image on the website. The problem with that, is that those images are much harder to change, take more time to download, and are not generally searchable by search engines.
In the last few years, it has become possible to use Web Fonts. These are fonts that are the same, or nearly the same, as the ones you could use in your word processor, but they can be downloaded as needed from Google or elsewhere.
Here are a few of our websites that are using Web Fonts:
And, of course, the site you are looking at right now. Most of these Web Fonts are free for personal and commercial use, but we had to purchase a license to use the one on Crafts.bz and on this one (JWebs.bz).
Also, our sites use FontAwesome, which is also a web font.