In Unix, how do you remove everything in the current directory and below it?

Practice safe computing. Simply go up one level in the hierarchy and don't use a wildcard expression:

cd ..; rm -rf -- <dir-to-remove>

The two dashes -- tell rm that <dir-to-remove> is not a command-line option, even when it begins with a dash.

Will delete all files/directories below the current one.

find -mindepth 1 -delete

If you want to do the same with another directory whose name you have, you can just name that

find <name-of-directory> -mindepth 1 -delete

If you want to remove not only the sub-directories and files of it, but also the directory itself, omit -mindepth 1. Do it without the -delete to get a list of the things that will be removed.