The answer to 'why is my toilet clogged' is that there are several common causes, including flushing too much toilet paper, a foreign object being flushed, or a buildup of debris in the pipes. The symptoms of a clogged toilet include the water not draining properly, the toilet backing up, or water overflowing when flushed.
In many cases, you can try to unclog the toilet yourself using a plunger or a toilet auger (also called a closet auger or plumber's snake). These tools can help dislodge the clog and restore normal flushing. However, if the clog is severe or you're unable to clear it, it's best to call a professional plumber who can properly diagnose and fix the issue.