To install a standard ink cartridge, simply press the ink cartridge onto the nipple of the feed until firmly seated. Gently write on a scrap piece of quality paper to begin the ink flow.  Sometimes you have to be patient here as it could take a minute to get the ink started and flowing.  If it is being really stubborn and won't start after a minute or so, give the cartridge a very gentle squeeze.  (Be very careful not to squeeze to hard, or ink will drip out of the nib/feed -- it's best to do this over a paper towel.)