Your fountain pen consists of four parts when assembled—the cap, the nib, the barrel, and the ink reservoir. Most reservoirs are either a piston converter, a cartridge or an ink bladder. The converter and ink bladder require fountain pen bottled ink. The cartridge is a self-contained, disposable unit filled with ink.
Place the fountain pen, nib first, into the bottle of ink until the nib is entirely covered (Figure A). Twist the piston converter counterclockwise at the top. This forces the air out of the converter. Then twist the top of the piston converter clockwise to draw the ink up into the converter. While holding the nib above the bottle of ink, slowly twist the piston converter counterclockwise until a bead of ink flows from the tip of the nib (Figure B). Gently blot excess ink from the nib with a lint-free cloth or blotter paper.
Remove the piston converter by gently pulling it away from the nib. Insert a fountain pen cartridge into the nib and push firmly until the cartridge seats itself. You will hear a small click. You can easily switch between bottled ink and cartridges by rinsing the nib and piston converter with cool water periodically.
This video below shows how to refill piston type of converters by placing the nib inside the ink bottle and twisting the converter.