Well one starts with an s, the other with a c... :P
They changed the command to clarify what it does, checkout was / is used for switching branches as well as branch creation but has connotations of doing some locking in the repo from older vcs software.... I think. the new commands are switch and branch. check the docs
Idk what the deal is with switch, I thought it wasn't supposed to be creating branches but right in the docs there's a flag for it???
Im the kind of user that just deletes .git and starts over when I f up the repo, so take my git advice with a tablespoon of salt.