Hemorrhoids, in the rectum, occur when the veins are not returning enough blood back to the heart. When this happens, the vein walls do not receive enough oxygen and release a substance into the blood that causes them swell and become inflamed. This swelling weakens them and their more likely to break when they are rubbed, like during a bowel movement.

If your stools are hard, you have a higher chance of breaking a swelling vein. For this reason getting your stools softer is one step in clearing your hemorrhoids. You can do this by eating a diet and using remedies that help relieve constipation.
Hemorrhoids, which are enlarged or swelling can exist,

On the inside just above the muscle that closes the anus and into to the rectum. They are near the surface of the rectum mucus membrane
On the outside, they occur on the skin that surround the anus and protrude or hang outward.

In a way, hemorrhoids can be considered varicose veins of the rectum. Just like varicose veins in the legs, the rectum veins become enlarged and come to the skin surface and bulge out.
Hemorrhoids occur when you are constipated for long periods, sit for long hours, lift heavy items, or are pregnant.

If you're constipated, you're probably having a difficult time having a bowel movement. And when you do, your stools are usually small, hard, and dry. If you have to push and strain or sit on the toilet for 10-15 minutes, then expect to have hemorrhoids at some point. Two to three minutes is all you normally need to have a natural bowel movement.

Over 85% of the population has hemorrhoids. Hemorrhoids are a sign that fecal matter is not passing through your colon like it should. Simple hemorrhoids are not dangerous to your health, but hemorrhoids that have been building for a while will cause you some discomfort, such as,
Mucus discharge

Bleeding showing up in your stools or dripping into the toilet water
Itching on the outside of the rectum
Pain in the rectum area and during a bowel movement
Pain in the rectum area, when you sit
Soft bulging area in the rectum or anus that give you a sensation that something is there

See your doctor if your hemorrhoids are painful, have excess bleeding, or stools have change in color from medium brown to dark brown or black.

Just be aware of any growth in the rectum, bleeding during a bowel movement, and a change in your stools color. Then take action to take care of these changes.