iCal is the Mac's built-in calendar applications. It's the easiest way to keep track of appointments, events, holidays and birthdays.
The Adress Book app on your Mac is a great and convenient way of keeping track of phone numbers, email addresses and other information.
We love Keynote — Apple's own presentation software. The application makes it possible to create incredible presentations with very little effort.
So you've learned how to install applications on your Mac. Now for the hard part: uninstalling the applications that you don't need anymore.