It is possible to forward all emails sent to undefined email addresses to a default or catchall email account. This is useful for advanced users who use scripts and filters to process the incoming email and who don't want to set up individual accounts for each email address.
For the average user, however, setting up a catchall address is not advised due to spammers trying to guess people's email addresses. Setting up a catchall address without some sort of processing on the incoming email would result in a lot of spam being received and taking up valuable space on your server.
If your administrator has given your the ability to setup catchall addresses, this video will show you how to set it up.