Tutorial Step 11: Assign Resources
You can assign resources to tasks from task view or from resource view.
In task view, you can select the task and then use the Task Assignments inspector to select which resources should be assigned to it.
Or you can just pop open the menu on the Assignment button in the toolbar.
In resource view, you can assign a task by dragging it from the Unassigned timeline into a resource's timeline.
Because the 
icon is turned on for the tasks' Duration field in the Task Information inspector, assigning multiple resources to a task can change its duration. For example, unloading boxes gets easier when more people help, so that task should get shorter when more resources are assigned. But showing an educational video takes the same amount of time no matter how many people attend; for that kind of task you should click the icon next to the Effort field so that the duration stays fixed and the effort value changes instead.
icon is turned on for the tasks' Duration field in the Task Information inspector, assigning multiple resources to a task can change its duration. For example, unloading boxes gets easier when more people help, so that task should get shorter when more resources are assigned. But showing an educational video takes the same amount of time no matter how many people attend; for that kind of task you should click the icon next to the Effort field so that the duration stays fixed and the effort value changes instead. 
When you assign resources, their names appear to the right of the bars in the Gantt chart:
