Youtube channel handle look - what is it?

It's your channel's unique @name, like @yourbrand. Shows up in your channel URL (the one ending in /@yourbrand), in comments and in Shorts, and people can tag you with it. Change it in YouTube Studio > Customization > Basic info. There's a limit on how often you can change it, and your old one can be claimed by someone else after a while, so pick something you'll keep.