Chain is on the smallest sprocket on the crank and on the largest sprocket on the rear wheel
If by "normal" you mean a bike with one chainwheel at the front and one sprocket at the rear, then it will have either a 1/8" or a 3/32" width chain.
The bent sprocket is guiding the chain diagonally causing it to be unparalleled with the front sprocket, you will either need to purchase a new rear sprocket or find a way to bend the rear one back straight
You might have to either lengthen or shorten the chain, depending on if you're getting a bigger or smaller sprocket.
First of all, the rest of the cycling community calls the thing by the rear wheel for sprocket, and the thing by the pedals for chain ring or chain wheel - but I understand what you mean. And only you can answer your original question, as it depends on how you want your bike to behave. If you want more top speed - go for a smaller sprocket. If you want quicker starts - go for a bigger sprocket. If you don't have one - read up on the specs for a bike for the type of riding you want to do - then get the same for your bike.
Sprocket and chain and what?
No way to tell, as it will be different depending on bike size and sprocket tooth count. Bike chains are always sold overly long and are then cut to size.
On the front it's usually called a chainwheel or a chainring, on the rear it's either a sprocket, a cassette, or a freewheel.
Press down the rear foot brake and use a breaker bar or large ratchet with correct size socket to loosen nut on front sprocket. (never use impact wrench NEVER EVER!)Once you get the nut broken loose. Unclip your chain and put the gear in neutral and pull the chain through and set it aside. Put clutch in first gear and continue to ratchet loose the nut. Loosen nut all the way. Change out the sprocket. Tighten nut as much as you can with bike in gear. Put your bike back in neutral and feed your chain around the sprocket pulling it through and resting both sides of it on the rear sprocket where you will reclip the master link. Meeting both sides of the chain on the rear sprocket will make it easy to clip as the rear sprocket holds your chain for you. Once master link in chain is clipped. Step on the rear brake and crank down to spec lbs on the front sprocket bolt. If you don't know the foot lbs.. just make sure its real tight. Your done!
you stupid diennie
The smallest sprocket is usually referred to as the "cog" and is commonly found on the rear wheel of a bicycle. It is designed to mesh with the chain and is typically the one with the fewest number of teeth among all the sprockets on the bike.
In the drive train you have the front chainwheel/ring and the rear sprocket that both engage the chain. The pointy bits on sprocket and chainwheel which allows the chain to grip are called teeth. The ratio between the tooth counts is what determines which gear ratio the bike has.