Oh this happened to me the other day. I have a salt water pool so I just put some in a bowl and dipped his paw in it. Then I applied a paper towel with a little bit of pressure. It eventually stopped bleeding.
You use baking soda - it stops the bleeding and wont infect it - that is normally caused when you cut their nails to short - you cut the bloodline in the nail - I do highly recommend baking soda