Here you may assign User Stories , Tasks and Bugs to team members.

Left area contains unassigned items, right area contains all team members. To assign User Story to team member do the following:

1. Select Iteration in drop down in left area
2. Drag User Story (User Story Name is draggable) -> user names will be highlighted
3. Drop User Story on highlighted user name, thus assigning it to the developer

Other options:

1. You may expand user to see all user assignements
2. You may assign task on pair.
   Step 1. Assign task on first developer (dev1);
   Step 2. Expand dev1, drag User Story and drop it on dev2
3. Unassign tasks by dragging it from user and dropping on Unassigned Items area