JDL,
First off welcome, there is no better place than this. It sounds to me like the model you got is a supermini. It probably is about the exact size as a regular cigarette. These typically hold .25ml of juice. the mini, like a 510 is about .5 ml and a penstyle is about 1ml. everything else is also proportionate to the three main sizes, battery, atomizer, cartridge and vapor production.
to fill most superminis yourself you will have to push out the little resevoir inside the cartridge/tip. If you drip juice all the way down to where it is inside some may go between the resevoir and tip and end up in your mouth when you draw on it. use a paper clip or something in the little hole at the end and push it out the top. find a lot of vids on youtube for refilling carts.
vapor production aside from what else has been posted here also depends on the juice itself. Even some brands produce different amounts of vapor. Prefilled carts are usually pretty weak.
Don't give up on the little guy, it's only doing what it can.
Congrats on joing the vaping community and best of luck!
As far as ordering from China, most of them use PayPal. I do not like PayPal. and shipping costs are outrageous as well as delivery time. There are many good suppliers here in the States. Spend some time looking at all you can find and you will find good deals and get products delivered in three days or less in most parts of the country by usps priority. $4.99 usually vs $15 from China.