But it leaks out of the tub faucet... I have the 3 turn type knob system.. one for the hot water one for the cold and the one that you turn so that it directs the water to the shower head... I am a single mother of 2 little ones... help me please" I have replaced the shower head thinking that might help... but it did not do anything

The center knob is called a diverter. The washer has to be replaced.

Remove to knob. There is a screw under the plastic cap.

Remove the plate that is against the tile. This may slide off or any screw off.

U will see a spindle that is held in by a nut. Remove spindle and replace washer.

Put back together . Should be good to go.

Chuck

Just wanted to add a little to what Chuck said. After removing the handle, stem cover and escutcheon, the first nut you see will be the stem bonnet nut. That keeps the water from coming out around the stem. The second larger nut is the nut for removing the diverter. You will probably need a special tool to remove the diverter stem, call a tub faucet socket or wrench. Available at Home Depot Lowe's and hardware stores.