Whether they're soft tip (preferable) or hard tip....you need to take that white tip off. If they're hard tip, they're glued on. Try to pry them off (gently) by sticking a paperclip or tweezer in the center hole and just work it around until the tip pops off. If you just can't get it off, you can still fill them...it'll just be a different process.
If you get the tip off, then hold the cartos at an angle and drip the juice right onto the filler. Do about 3-4 drops, then turn the carto a quarter turn and drip about 3-4 drops, then turn it a quarter turn and drip about 3-4 drops....etc. The point is to soak the filler, but avoid getting juice down that little center hole. Let it soak in.....I actually put my mouth on the top and gently blow on it....it pushes the juice down. When the liquid is no longer pooling on top, drip some more onto the filler...again avoiding the center hole. The first time you fill one, it should hold about 25 drops or so. Instead of blowing on it to blow the juice down, you can shake it down...or just let it sit a minute or two until it soaks in. After you have about 25-28 drops in it, replace the white cap. Wipe down the thread end and screw it on.
There are other ways to fill them, but that's my way. If you can, do a couple at a time so that you can let one sit awhile. It'll soak in better if it sits. I fill my cartos the night before to take to work the next day.
Some are just easier than others......
