This first tool is to figure out fonts being used across a website. It's very straightforward too. Here's a quick HTML lesson though:
Hypertext Markup Language (HTML) is a "markup language". It's used to display content in a web browser. HTML is.. structure. Think of it as a skeleton. HTML makes it possible for browsers to read content in a structural manner (which also makes it extremely helpful, specially to folks with visual impairment.
I'm sure you've come across HTML tags before, some of them might include h2, p, button, and so on. Generally, text is divided into headings (which there are 6 of: h1, h2, h3 ...), and paragraphs.
The reason I've explained all this is to understand how FontOfWeb works.