If your ego charger is the same as mine, it will have a little red light that turns green when fully charged. One of my Batt's I started vaping immediately since they come with a bit of a charge from the factory. The other one I charged till the light went green. I haven't noticed any difference in performance.
Concerning the cartomizers, all you do is unscrew the ego-t Atty from your battery, and screw the cartomizer onto it. You can vape the carto directly, but many prefer to put a drip tip on it. (I do, but only for comfort. Its not needed to vape)
Look up some carto filling methods. The most common are the condom method, the taryn spin, and the syringe method. I use the syringes method because its quick, easy, and not very messy IMO. Be sure and stick the needle between the batting and the carto wall if you use the syringe method. If you didn't order a syringe you can get one from a drugstore or tractor supply/pet supply store. If u aren't interested in a syringe, you can just drop juice onto The batting, let it soak in, and repeat. Standard cartos hold 18-22 drops (fill till the top of the batting looks wet, blow out onto a paper towel, and vape)
Sorry for long response. I'm at work and bored
P.s. the carto filling methods can be seen on YouTube. Dont let my longwinded response deter you, they are actually easy to fill.