Clay:
The pump is so you can use ink from a bottle as opposed to the cartridges. You can fill the pump reservoir by dipping the end into the bottle and turning the screw thingy on the other end, wipe it off then stick it on just like you would the cartridge. Or, my preference, is to install it empty then dip the nib into the ink bottle and fill. It's the same concept as the old fountain pens before the ink cartridges came along.
I recommend Private Reserve brand ink in bottles or cartridges. It's just a little more expensive, but much smoother flowing and better writing. Google for it, lots of folks sell it over the net but it may be hard to find locally. Comes in a ton of colors.
The Baron makes a very nice pen in roller ball or fountain pen.