SAP Basics - Applying a License to a User
Taken from: http://help.sap.com/saphelp_sbo882/helpdata/en/45/06da50d8696c30e10000000a114a6b/content.htm?frameset=/en/45/06434daaf40485e10000000a155369/frameset.htm - this is pretty key for day-to-day life with SAP-