Objective 1.1 - LUN Masking and PSA-related Commands
What is LUN masking? explains what LUN masking is in layman’s terms (in case you have a NAS only background). See Storage Masking? for the Yellow Bricks advice on LUN masking.
For an overview of PSA and commands, see VMware vSphere 4.1 PSA.
Also see the vSphere CLI guide, vSphere Command-Line Interface Installation and Reference Guide.