How are mozzarella cheese sticks (string cheese) formed?
Oh you mean cheesesticks not the fried mozzeralla sticks.

I would imagine you would knead it by using the folding method in which you flatten the cheese and fold one end of the cheese over to the other end and continue folding it in that fashion(and the same direction). 

Also note that the mozzeralla sticks you buy at grocery stores are machine processed and you can't really hope to achieve that same results/texture.