How do I get a steam account?

Okay I feel really dumb. I downloaded and ran the Steam installer. It wanted to verify my email, so I entered that. Then I clicked on the link in the email. Took me to a web page that said I was verified. Great.

Now what? I still don't have a username or password. I can't log in without that. How do I get a username and password? ELI5, please.