Note: If your users want to set up aliases for actual Google Apps email accounts, read how to forward Google Apps email to a personal email account. The steps on that page must be done by the account holder; they cannot be done by you in the dashboard. Please note this is only possible after Google has verified the domain.
You may want to set up email aliases, or what Google calls Groups, for two reasons. One is that you only get a certain number of email addresses with your Google Apps account, but you need far more addresses. The other is some people don’t want another email account to check but simply want email sent to the team address to forward to their personal address.
For example, suppose you want to create an alias for email@example.com that forwards to firstname.lastname@example.org. (Note: Your DNS changes must be in place and Google must have verified the account if it is brand new before following these steps.) Once you log in to your Google Apps account, read how to Create a group. Click "Create a group with the Admin Console" once you load the article and follow the steps there.
Once all those are created, each person will need to add that alias to their account so they will appear to be sending everything from the team domain, such as swimteam.org. Read sending mail from a different address to learn how.