Hahaha, you're so funny! LMAO!
Man, you've got to think digital, rather than analog. Don't think about water flow, a good analogy for analog.
You need at least 3 NIC cards to share Internet. You may be able to share files between your 2 PCs with a network cable and 2 NICs, but not Internet. Go buy a router or hub and read the instructions. It's EZ 2 do.