Questions about mail sever

Hey geeks I have alot of confusion about how to set up our mail server!

We have a domain set up to use the DSN provided by network solutions, and have it point to our WAN IP in here in our small office; we have a Dell Server running Windows Server 2003, and got the ISS working and everything.

I know windows server 2003 has some type of mail server built in, and we also own a copy of Microsoft Exchange 2003 Server Standard; but not sure what it does, how to use it, or why to use it.

We want to use outlook and the email @ourdomain.com along with our calendars and such.

Anyone know the best solution?

Thanks!