To answer your questions,
1) That little bit of paper on the end of the joint is most likely a result of weed falling out of the tip as you were rolling it, which isn't a big problem, however I recommend cutting it off before you spark up, to avoid getting a hit of pure paper.
2) Yeah, the other end of the joint, the end you suck through, is pinched shut, but remember that air as well as smoke are made up of minuscule particles which can easily permeate a space much smaller than can be seen by the naked eye. If the joint is well rolled, the hole on the end you smoke from should be just tight enough to hold back the actual physical bud from sucking into your mouth, and you should have no problem inhaling a nice full hit of reefer.
3) Yes, if you are already high enough to make you happy, you can put your joint out, and smoke the rest later.
4) It stays lit like a cigarette, for a certain amount of time. However the fuse is much shorter than that on a cigarette, as a cigarette will burn to the filter regardless of whether or not you smoke it, while a joint will stifle itself out after about half a minute.
Hope this helps
