You can setup multiple email accounts in Microsoft Outlook using the menu Tools - E-mail Accounts...

Select Add a new e-mail account.

Click the Next button and configure appropriately.

Repeat this for each e-mail account.

You will be able to retrieve mail from all accounts in your inbox.

One of the accounts will be considered the default account when composing new mail, but using the Accounts button on the toolbar, you can send from any of your configured accounts.