The crimson part contains the aerometric filler. Essentially it's a sac that suctions in ink through the nib. The Silver part in this picture
Contains your feed and nib and is referred to as a whole as the section.
When you first get a fountain pen, new or not, you should always flush the pen. This means you submerge the nib in water with a bit of dish soap. There's other ways to clean and flush the pen but this is the easiest way. For new pens, this is to clean out any machining residues or chips. For old pens, it's to clean out old inks and whatever else is in there.
What I would do is, reassemble the pen. Then squeeze and squirt out water like 5-10 times. Then take the pen apart again and submerge just the section (the silver part in the picture above) in water up to the end of the nib (the metal part where you write with). Let it sit overnight. Then wipe it clean, then assemble it and squeeze in and squirt out clean water again.
So you don't need a converter or anything because that button you're pressing down on is a ink hold mechanism called an aerometric filler. To fill the pen, you'll submerge the entire nib up to the section then press on the bar like 5-6 times. Wipe it clean and write. I highly recommend Noodler's and Diamine Inks.
Check out
these videos from Brian Goulet for more information on the basics of fountain pens.
