In addition to using the Assign Resources dialog, you can also assign resources by using the Resources tab on the Task Information dialog, or by using the controls on the Task form.
Assigning Resources with the Task Information Dialog
Double-click on the task to which you want to assign resources.
Select the Resources tab.
Select the resource name you want to assign by clicking the drop-down menu that appears when you select a row in the Resources section of the dialog.
Edit the Units value if necessary.
Repeat steps 3 and 4 for each resource you want to assign to this task.
Click OK to assign the resources.
Assigning Resources with the Task Form
From the Gantt Chart view, click Window, Split to show the Task form.
Select the task to which you want to assign resources.
In the Resource Name field, select the resource you want to assign.
Edit the Units value for this assignment if required.
Edit the Work value for this assignment if desired.
Repeat steps 3 through 5 for any additional resources being assigned.