How do i get electric bike to spin the chain?

i wanted to make an electric bike but i dont know how to make the chain spin... how does it work?

does electricity and battery make it spin or what how does this all work?

You are right. An electric motor and battery are what is needed.

But most electric motors are either direct drive in the rear hub OR there is a roller that drives the front wheel directly. With your level of expertise I'd recommend getting a kit. Australia do some good ones.

Been doing some web research on this recently. There are several possibilities.
Motor can drive the wheel through a roller(either front or back).
Motor can be built into one of the wheels.
Motor can drive through the gears.

If the motor drives through the gears, then they may include a freewheel mechanism so you do not have to pedal when the motor is running. Usually, the geared ones appear to lose some gears as they connect onto one of the crank gears. Not sure of this, though.

Batteries are the key to performance. Lead-Acid batteries of the AGM type are the cheapest but they are heavy and give the least range. Current top performers are Lithium nano-phoshate batteries but you will find them expensive. As usual, it is a cost/performance balance that determines if they are economic.

The motors come in either brushed or direct drive versions. Direct drive should have the better life and performance. Both need a controller to operate. The controller has inputs from a speed controller (usually a twist grip) and overide switches on the brakes which cut of the power when braking.

Quite a lot of money is tied up in the batteries (especially if you use Lithium nano-phosphate) so the batteries are quite often in a compartment which can be removed from the bike for security reasons.

Hope this gives you a few ideas.