Welcome! This website is (quite obviously) a small text generator.
It's fairly self-explanatory - you put some text in the first box, and it will convert it into three different small text "fonts" for you.
To be clear, they're not actually fonts. 
You can tell they're not fonts because it's possible to copy and paste the small text generated into other websites (like your Instagram bio, a Tumblr post, etc.). 
You wouldn't be able to do that if it was just a font. So how is this copy and paste stuff possible
Well, to answer that question, we need to learn a little bit about Unicode.