How do I set up post by email?

My host provider set up the mail server to his server, and provided a login name and password. However, the Wordpress instructions say:

Any mail received at this address will be posted, so it’s a good idea to keep this address very secret. Here are three random strings you could use: H4dbwoDO, lZalUf8H, S1Uxtj2L.

The login name to the email is:

I don't understand what to do with those "strings"? Sending an email to is not working to actually put a post on the site.