Step One:  Gently unscrew the section from the reservoir.

 Step Two:  Align the ink cartridge with the section as shown.

Step Three:  Press the cartridge into the section until you feel it click into place

Step Four:  Replace the section back into to the reservoir.  Your pen is ready to write.

Note:  It will take a minute or two for gravity to pull the ink to the tip of the nib.  Do not tap the the nib on the writing surface to expedite the process as this may damage the nib.