What do you use Microsoft Outlook for?

Email, I have never used it.

The difference between Microsoft Outlook and other email programs like Outlook Express or Thunderbird, is that Outlook also has an integrated Calendar, Notes, Task list, etc. Microsoft Outlook is considered a "Personal Information Manager", not just an email client.

Outlook can also integrate with Microsoft Exchange (if you work for a medium to large company you may have Microsoft Exchange as part of your email system) which the others cannot... at least not easily or as well.

edit: what the heck did i get downvoted for?

Outlook is more or less the Business Version of Outlook Express with several other features that are used in a Business enviorment, with calander,appoinments and tons of other features, to many to mention here. Go to Microsoft and read the FAQ.

Email. You can use it to set up accounts, including Hotmail and others and use that to check them.