When your cartridge is empty take it out of the printer and put it on the refill pedestal that you may have been sent with the kit, if not rest the empty cartridge on a surface that has been carefully protected and covered with an old cloth.
You now need to make a hole in the top of the cartridge so that you can insert the ink. Take care when doing this to avoid any injury. In certain kits your pedestal will have a special instrument to make the hole, however if you are not using one of these then a sharp thin object will work just as well. Do not use something which you do not wish to get dirty!
Once you have the hole in the empty cartridge you should use the syringe like tool in the refill pack and insert this into the cartridge whilst filling it with new ink. Once it is full, which should not take very long, put the newly filled cartridge back into the printer.
Once you have inserted the cartridge into the printer, switch your printer on and allow it to realign the cartridges. This should happen automatically, if not you can manually instruct the printer to do this through the printer options on your computer.