I fixed the bike rear tire and I dont know how to put the chain back on. Please help. Is the any online manuals?

raise the back of the bike and put the wheel between the rear stays place the chain on the freewheel, and pull the wheel back and
then just tighten the wheel nuts.

If it has only started doing it with that tyre, then it is possible that that tyre is not compatible with your bike. Sounds silly, I know. But bikes are strange animals, and some tyres will create speed wobbles and vibrations and when you change them over to another brand it all goes away. Take it back to the people who fitted the tyre and have them check it out. If they find nothing ask them to fit another brand of tyre to see it that cures the problem.

That's why there is an internet. Search for 'how to replace rear wheel" and look at the hits that apply.

hi, it sounds to me like the bike has been ridden hard and needs the chain replacing due to it strecthing. on the swing arm at the back is their two bolts sticking out the end of each swing arm their should be one in one side of the swing arm and one in the other side of the swing arm, this is right at the very back of the swing arm.
if you find these then these are the adjusters for the back wheel you then need to loosen the back wheel bolt but dont take it out then adjust these adjusters by the same amount do it in half a turn a time you need to do both the same else the back wheel wont be level keep tightening them in and this will then pull the wheel back and this will tighten the chain if its all ready adjusted fully then the chain is scrap and needs replacing, if you dont have adjusters then the chain needs replacing, it will keep coming off if its slack

you can cause damage to the bike if the chain comes off whilst riding at speed so it may be best to get the chain before you use the bike

Does your bike have a derailuer? (gears) If so, check that the chain is running though it correctly. Also check that your wheel is aligned correctly, you can check this by simply lifting the rear wheel off the ground and spinning it. If the wheel rubs on your frame, then simply loosening the bolts and tightening them up when the wheel is straight should fix the problem.
Cheers.

Look at this so you have a handle on what the shrader valve looks like.

Put the parts together as follows: insert the hard plastic piece so it protrudes to depress the center valve in the tube; place the round rubber piece over the frist piece wih the large opening facing outward toward the tube; snugly screw on the cap to compress the first two pieces.

Does the rear wheel go on such that you can adjust it to take any play out of the chain? If so, turn the bike upside down or put it on a bike stand. Loosen the back wheel and pull it so that the chain is tighter and then tighten the wheel. There are other possible causes but I suspect this since you recently removed the wheel. Also I'm not sure how often the chain falls off. If this doesn't work, ask again and let us know how often its coming off. Good luck!

This is how to fix the tire:http://www.youtube.com/watch?v=pzr_RGTWWoc I unfortunately haven't seen any good videos on rear BMX wheels and tires. If you already have the wheel off, you can just follow the video and then reverse the steps you took to remove the rear wheel. If not, you will first have to make sure all the air is out of the tire. Then if there are stunt pegs on the rear you will need a deep socket that fits the wheel nut and an extension bar and ratchet wrench. The reason to have the tire flat when removing and installing the wheel is so you can get past the brake pads if you have rear brakes. If you have pegs it is easier to remove them completely so you can unhook the chain from the rear freewheel. When reinstalling the wheel, you have to apply tension to the chain by sliding the wheel back before tightening the nuts. It is easier if you center the wheel and tighten the nut on the side opposite to the freewheel just snug enough so the wheel won't move forward. Then put tension on the chain side and tighten that nut. Alternate this procedure until the wheel is centered and there is proper tension on the chain. Proper tension is when you back pedal by hand and it feels smooth not stiff and the chain does not sag.Once the wheel is installed with a new tube or both a new tube and tire you can look on the sidewall of the tire for how many pounds of air to inflate it to. I know this sounds confusing and it is tricky to do by yourself but once you've done it successfully it becomes easier each time. If you don't have the tools it is easier to have it done at a local bike shop. It is worth the money.Here are a couple more websites to search through for more information:http://www.parktool.com/repair/readhowto.asp?id=144 and http://sheldonbrown.com/gloss_e-f.html#flatland I hope this helps and please get back to me if you need more help.

off of wat bike. if a dirtbike, loosin up the rear axle bolt, slide it out and pull the chain to the left and spin the wheel in the right direction, then jiggle it loose. take the caps off of each side right away so u dont lose them.of course i dont no wat bike u got tell me that and il 4sure help u

Your chain problem is probably because your chain is not tightened and maintained.
You should clean your chain after a ride, and oil it (very little oil).
Good luck