Many vanity and tub/shower faucets have rubber parts (washers, o-rings) inside the main valves that wear out every few years. If you find that a faucet still drips when turned off, then you likely have some rubber washers and/or o-rings that need replacing.
The most common culprit for unwanted water usage is found in the toilet tank, which is found at the back of the toilet under the porcelain lid. There you will find a toilet fill valve, which automatically allows clean water in to until a set shut off point to serve as the next flushing water. Also, you will find the flapper and flush valve which actuate the flushing action and controls water the water level in the tank. If you hear a hissing sound that does not stop when the tank should be full, you likely need to address the fill valve.