Refilling cartridges yourself has a learning curve, although not because it's rocket science! But when you're learning it can be a bit messy. You'd do well to wear a pair of lightweight, disposable gloves, some refill kits include these. Spread newspaper on your desk.
Yes, step-by-step instructions are included in the pack. They don't usually tell you the quantity of ink needed in each cartridge. You fill the syringe, making sure there's no air bubbles. Insert it into the correct hole - for the colour - push the needle all the way down in the sponge. Withraw a quarter of an inch (old money) then slowly squirt it in, until it stars to come back out the hole. Then stop and using kithen paper, soak up the excess.
I have one syringe for each colour and I mark them with a sticky lable. If you don't use all the ink in the syringe, leave it in it - storing them needle up - or squirt it back in the bottle.
Don't do it in your best clothes, for nomatter how often you do it or how carefull you are, you're sure to have an accident sooner or later. I live in rented accomodation and the cream carpet now has a rather interesting pattern in blue and red. But if you catch a spill quick enough, you can mop it up, as it's water soluable. Remember to have everything you need close at hand.
It isn't really that difficult, once you get used to it. Tell me though, why weren't you using clone ink, that isn't expensive and is better than paying through the nose for a branded one. Also you can now get Continuous Ink Systems 'CIS' they are a doddle to install and top up and megga cheap now.