If you have a flood in your basement, there are a few things you need to do. First, turn off the power to the basement. If there is water in the electrical outlets, you don't want to risk getting electrocuted. Then, start pumping out the water. You can use a wet/dry vacuum or a sump pump. Once the water is out, start cleaning up. Throw out any items that have been damaged by the water and mop up the remaining water. If you have a finished basement, you may also need to dry it out. You can do this by using a dehumidifier or fans.