In the Nonprofit Starter Pack, the Opportunities tab has been renamed to Donations. You can change this back, or to whatever name you want. 

Go to Steup > Customize > Tab Names and Labels > Rename Tabs and Labels

Select Opportunities and enter the name you want.

To have different "kinds" of Opportunities, most groups use Record Types. You might want record types for Gift, Grant, and Purchase. Again, do whatever makes sense in your situation.

Check the Salesforce.com help for working with Record types--there is lots of good information there.

Hope that's helpful,
Steve