Article: Time and Money options in the Resources tab
The Availability column provides the option to specify how much time a Resource is available on the project Schedule. For example, if a Resource is splitting time equally between two projects then the availability (for task assignments) on each project is limited to 50% when managing each day's "Work" allocation.
You can also add the "Bill Rate" column to desginate the per/hour rate for a Resource. The "Labor Cost" column in the Tasks list will calculate this rate with the value in the "Work" field to give you a total Labor Cost for any tasks assigned to that Resource.