A bowel movement is the end result of eating. Food passes through your stomach on its way to your intestine where it's broken into its nutritional components. Those components are absorbed through the small intestine and delivered to the rest of the body. Leftovers go into the large intestine where fat and water are absorbed.
The rest, deemed useless by the body, is excreted as stool. It's a combination of fiber, bacteria, cells, and mucus. And it tells you so much about your overall health it's weirdly fascinating.
On average, good stool from a healthy body should come once a day and be brown, smelly, and smooth. But you might not be average, and that's ok! It's so important to know what YOUR normal is so you know what's ok to see in the toilet and what isn't.
National Institute of Diabetes and Digestive and Kidney Diseases: The Digestive System & How it Works
WebMD: What Do Different Poop Colors Mean?
Everyday Health: 11 Icky But Interesting Facts About Poop