From a public health perspective, the main points are:
About 49,000–50,000 Americans die by suicide each year.
That works out to roughly 135 deaths per day.
For every suicide death, there are many more suicide attempts and many more people who experience serious suicidal thoughts.
Suicide is among the 10–15 leading causes of death overall in the U.S., and for some younger age groups it ranks much higher.
Researchers study suicide to understand why it happens and how to prevent it. Factors that increase risk can include:
Depression and other mental illnesses.
Alcohol or drug misuse.
Chronic pain or serious illness.
Social isolation and loneliness.
Major life crises, such as the loss of a loved one, financial problems, or relationship breakdown.
Access to highly lethal means during a crisis.
One important finding is that suicidal crises are often temporary, even when they feel overwhelming. Many prevention efforts focus on helping people get through those periods safely, improving access to mental health care, strengthening social connections, and reducing access to highly lethal means during a crisis.
If your interest is historical or sociological, I can also explain how suicide rates have changed over the past century, why they differ by age and sex, or what researchers have learned about preventing suicide.