Flea dips have different active components than flea shampoos. They also work differently. Dips for fleas are generally made with a little water, then applied to your dog's coat and left there.
You can use a sponge to apply the solution. Some formulas can be applied to the skin directly, while others can be combined with one gallon of water.
Use an appropriate amount according to the instructions on the flea dip. If you use too much, it might irritate their skin.