The fuel pump has three ports. Two of them next to each other and I need to know which line goes where.

Hi,
I put up a picture of the most common pump use now. I is a plastic-bodied Mikuni used on many makes.
The line with no arrow attaches to the fuel source(tank), the solid arrow to the engine for vacuum to make the pump work and the dashed arrow connects to the carb.
If you have a metal-bodied pump, the concept is the same.
Often there arrows on the pump itself identifying in or out; vacuum is unmarked.
Peace,
Clarke