VM Player runs a virtual instance, but can’t create the vm. [Edit: Now it can.] Workstation allows for the creation and administration of virtual machines. If you have a second machine, you can create the vm on one and run it with the player the other machine. I bought Workstation and I use it setup testing vms that the player runs. Hope this explains it for you.
Edit: According to the FAQ:
VMware Workstation is much more advanced and comes with powerful features including snapshots, cloning, remote connections to vSphere, sharing VMs, advanced Virtual Machines settings and much more. Workstation is designed to be used by technical professionals such as developers, quality assurance engineers, systems engineers, IT administrators, technical support representatives, trainers, etc.