Once you remove the supply tubes, flexible or otherwise, you are ready to take out the faucet. The first thing you do is unscrew completely the lock nuts that hold the faucet to the sink. Carefully remove the faucet from the sink. You'll want to avoid damaging the sink surface by putting down some masking tape. You will also want to clean away any old plumber's putty or sealant from the sink. A putty knife is best for this job. If you still have stubborn spots of putty hanging on you can use very fine steel wool or a scratch pad to get it off. Now you are ready to drop in the new faucet. Line up the spray hose and any supply tubes, if any, and place them into the proper holes. If your faucet has copper supply tubes sticking out of them, be careful not to kink them. Most faucets these days are sold with a gasket under the faucet's deck plate to provide a watertight seal. If you want, however, you can put a ring of plumber's putty or silicone around the holes of the sink and the underside edge of the faucet plate. If you want to be the prefect plumber you can also put a bead around the edge of the faucet deck plate after you've tightened it down.