You get a clog when the toilet bowl fills up and fails to empty, which is fairly common and easy to spot. Most common toilet plumbing problems can be easily identified by yourself, however the prevention or solution should always be carried out by a certified plumber.
An obstruction is typically brought on by a combination of paper and human waste. A plunger can usually unclog a clogged toilet. If that doesn’t clear the clog though, then a sewer snake or drain auger can be used instead.