Drums are a very loud instrument. It is also the only instrument that does not need amplification. Drums are used across all music genres (except dj). They typically come in 5-piece sets with 2-3 cymbals. Here is an example:
They are typically played in songs but are also for fun. I have one in my house. They are loud. They are a very crucial instrument to keeping a beat. Almost no band can exist without them. They are so important, that there are mostly 3-4 people on a band(drums, bass, guitar, voice).