If there are 7 students in a class to make a team 2 names are drawn how many different teams can be possible

The first name can be any one of the seven.  Then for each one . . .
The second name can be any one of the other six.

Total number of ways to pick 2 names = (7 x 6) = 42 .

BUT ...

If you pick Tom and then Jim, you have the same team as when
you pick Jim and then Tom. 

Out of the 42 different ways to pick 2 names, each different team
can be picked in two ways.

So there are really only ( 42 / 2)  =  21 different teams possible.