Kerning type is moving individual letters such that the space between them feels right. It’s not something you have to be terribly concerned about with web type generally, but it’s still a good design skill to have for working on type that is quite large or long-lasting like a physical sign, logo, giant headline, etc. This game is a fun way to practice.
Wanna be a better web typographer?
It was once famously said that the web is 95% typography. You can't be a web designer and ignore type! We have an in-depth course on web typography from Jason Pamental getting into things like responsive styles, variable fonts, font loading, and more.