The plumbing courses cover all the aspects that you will be required to deal with as a running toilet. You will be taught about the basic aspects as well as about health and safety issues and sanitation.
With a putty knife, carefully scrape the remaining parts of the wax ring from the area. Clean the spot so that the new wax ring will be level. Place a new wax ring on the opening and replace the toilet. Bolt it back onto the floor, reconnect the water line repair supply tube and watch for leaks as the water is turned back on.
In repairing a tub faucet, you will notice that there will be drips that you need to address to. With this, you will need to replace the washers and/or seats.
Working on the gas lines is also a complex job that only a licensed plumber can handle because it is very dangerous. Small leaks can't always be detected by odor alone, but a licensed professional has the proper equipment that's needed to ensure that you don't have any leaks in the line.
As with anything, when you are not sure how to fix a plumbing issue and when you don't have the proper equipment, you should contact a professional. They can usually find out what the problem is and resolve it for you in a short period of time. They will also be able to tell you if you have any other problems and water line repair they can suggest resolutions.
Keep your hands clean and dry. Plumbing jobs get slippery, so it's important to work with a pair of sturdy gloves so you don't lose your grip and accidentally hurt yourself or break something.
Is your garbage disposal clogged, but it is turning ok? This may be due to a blockage in the pipe. If you look at the pipe work under your sink you will see that the disposal is connected to a pipe that should join to a U bend and providing it was installed correctly it should have a connector that can be undone. If you undo this connector the pipe will pull away and generally this is where most blockages occur. Remove the blockage and reconnect the pipe.