There are other skills plumbers need aside from being able to work with water. One of the most common things that a drain line repair on is fixing water lines.
When you get to the house stand if front of the toilet and locate the water shut off valve. Should be down below the toilet on the wall. Just turn it off (righty-tighty) completely and flush the toilet. All the water should have left the tank, well at least most of it. If there is remaining water line repair get it out with paper towels or a rag. The important thing is that no more water came in. If it did then your valve is not shut all the way or not working and you need additional help.
After you have the stems out you should be able to find the washer on the "inside" end. If it is nicked, torn or brittle it is likely the cause of your drip. Even if it looks brand new, go ahead and replace it. You've already come this far. You can get replacement washers at almost any hardware store. Sometimes you may want to replace the whole stem, especially if the handle end is stripped out. It's best to just take the stem with you to the store and see if you can match it up. Most Do It Yourself stores have replacement stems for many popular brands. If your valve has a center diverter valve to switch the waterfrom the tub spout to the shower head the same process applies. Many times it is easier to replace the diverter stem than to repair it. This really depends on the design of the stem.
Depending on your repair job you might need a bucket that will fit below the sink trap, as well as some rags and newspaper. Masking tape is useful for labeling and for wrapping around the heads of the wrench to protect your chrome tap handles. Rubber gloves are recommended, particularly when working with the toilet, but there are greases and glues that you may not want on your hands.
Be certain that the bathroom exhaust fan vents to the outdoors, not into the house or attic. If the exterior vent dampers don't operate properly or water line repair don't seat well have them fixed or replaced.
Plumbers, contractors, landscapers, and related professionals are often indexed by numerous online websites eager for you to visit their "directory". Each field will have their own group of websites competing for your attention. In the end these "Plumbers Directories" are often incomplete, and frequently provide little more information than the phone book.
By the time that you have made your pick, make sure to check ID and Certification. Remember, these individuals will be doing their works inside your home. The security of your family is also an issue here. If they can't present any papers of identification, then don't take them in! When it comes to your family's safety, there's no room for experiments.