Work Item People
The people tab on the work item for lets you add the following information:
- Owner
- Team
- Assignees
- Followers

Owner
This is the person who is responsible for the work item. There can only be one owner.
Team
A team can be assigned to a work item. This can be useful if you don't usually assign the work item when it's created, and instead let the team decide later who will work on it. The team field can be disabled on the Admin/Work Item Types page, so if you don't see it, then that's why.
Assignees
You can assign any number of people to a work item. You can also add an "assignee" that only includes a work role, but not a member. You might decide later which person will be assigned to the work item. Notice that you can also give each assignee a time estimate. This time estimate information is used on the Schedule page to show employee utilization.
Followers
A follower is anyone who wants to receive notifications about status updates to the work item.