From Assets, Select Fleet.
Then from the left hand side of the screen highlight the unit that you wish to assign a crew member to.
In the lower right hand side of the screen, make sure you are on the Crew Assignment tab.
Once you are in the Crew Assignment tab, right click anywhere in the grid.
Select Assign Crew Member
Select the employee from the drop down list.
You can then choose the employees' role (ie: Operator, Oiler, Laborer, etc).
Then select the date that the operator started running the equipment. The default date will be the day you assign the operator.