Once you have setup an email address you will want to setup your desired email software to use that new email address. This tutorial shows how to configure the popular Outlook Express email software supplied with windows.
Open Outlook Express and click on the top menu item called "Tools" and then click the "Accounts" option:

You will now be shown the Accounts screen where you will need to click the 'Add' button:

You will now be given a series of simple questions to answer about your new email account.
You will need to enter your name, the email address you are setting up, and the mailserver information found in your UnitedHosting welcome email. The mailserver is always 'mail.yourdomain.com' for both incoming and outgoing mailservers:



Next it will ask you to enter your account name and password. This is again your email address you are setting up, and the password you chose in your control panel when adding this email address:

Once you have entered the above information you can click on 'Finish'.
You will now see the account you just created inside the accounts list. Select the account and click on the 'Properties' button on the right hand side, and then in the new window that will pop up select the 'Servers' tab:

On the above servers window, make sure you tick the option for 'My server requires authentication'
Then click 'OK' and close all the windows as you are done!
You can now send and receive email from your new email account in Outlook Express.