What does a custom domain do?

Does the custom domain thing let me change something from nifty-papayay.glitch.me to mycustomdomain.xyz
?? Is that how it works??

Yes. Custom domains allow you to use a domain you’ve purchased and have your Glitch project site show up when you go to yourdomain.xyz.

Yep! You can learn more about adding custom domains to a project here: https://glitch.com/help/custom-domain/