The most important thing is to know where things go in your HOME Folder.
All your personal stuff goes there in one of the existing folders or new one's
that you create for special use.
Documents, Pictures, Movies, Music, Web Sites, your personal Library of preferences and application support files, and your Desktop, it's all there.
You will also notice that there is a System Library when you open your hard drive icon, but that's for system wide preferences and support files for all users.
Many users are fine using the Safari browser, but many others download Mozilla FireFox or Camino.
Once you have everything set up the way you like it, there won't be much else to do except for occasional software updates.
I do strongly recommend setting up your system with a secondary Super User Account for all your normal daily tasks.
Your primary administrative account should only be used for installations
and maintenance.
Just open System Preferences in your dock and click the Accounts icon.
Your original administrative account is usually in your registerred name.
Your Secondary Super User Accounts need to use a different identity.
This is important because your strongest defense against security issues is to limit installation privileges.
Unlike Windows .exe files, nothing can be installed on your computer
without the administators password or by using a drag to Applications
install while logged on as administrator.
There's a wealth of information in these forums, so if you have any trouble at all, someone here can help you with a solution.
Reading through the Macrumors starters guides helps to get you though a lot of basic questions.
http://guides.macrumors.com/Mac_Beginner's_Guide
There are also guides for just about any issue that may come to mind.
http://guides.macrumors.com/Category:Guides
Enjoy and welcome!!!