I just recently bought a new tanks and it didnt come with a hood but it did come with a light.how do I put the light on the tank without a hood?
It depends on the light fixture, but you can get 'stands' that clip onto the glass to support the light.
Some light fixtures have slots for legs that will sit the fixture on the ends of the tank and keep it raised a couple inches above the water. Another option is a glass top that will cover the tank and you could just sit the fixture right on top of it. They also come with a length of plastic that can be cut to allow room for a filter or anything else that's hanging off the back of your tank. This way the top stays tightly closed for fish that may try to jump out.
I had a piece of plexi-glass cut for my 55 gallon tank, and it works great. It only cost $7