Claim more than 1 when single

How is it possible to claim more than 1 when filing as single?

 

I get confused on this because only understand that I can only claim 0 or 1 as a single person. What allows a single person to claim more than and what des that mean when I claim 2 or 3 because I see this was suggested to me with the calculator. Please clarify what the number means as I increase it.