Lesson
This is a useful, but tragic, word in English. (Tragic means "very sad")
To "commit suicide" means to kill yourself on purpose. Some people do this by getting a gun and shooting themselves, some people jump off a building, some people jump in front of a moving car. You get the idea. People who are very depressed or very upset do this. It's rare, but it does happen all over the world. It is an extremely sad thing when this happens. But anyway, it's an important word in English and it has some other uses as well.
Just today in the USA, some people were killed at the Boston marathon. That is a big running race. The people were killed by a couple of bombs. We still don't know exactly what happened, but there is a chance that the bombers were "terrorists" and it's very possible that the terrorists killed themselves too. If you kill yourself while killing other people using a bomb, it's called a "suicide bomb". It's much easier to use a bomb in this way because if you are willing to commit suicide, you can be right beside the bomb when it explodes. It is absolutely horrible to think of actually doing this, but this is what happened in 2001 when the planes flew into the buildings in New York city, and it's quite possibly what happened today.
Here is a video that explains all the meanings of this word very clearly:
Learn American Slang and Vocabulary
Again, it's not a happy word, but it's one with many uses and it will help your English if you understand the deep meaning in detail. I hope this helps.