I'm not sure why people are downvoting this, but I'll give you a quick rundown :)

Pompeii was a city a wee bit south of Rome which took advantage of both the rich volcanic soil offered by the nearby volcano, Vesuvius. It was extraordinarily prosperous, and became well known as a tourist destination - think of Las Vegas - especially for the wealthy.

On August 24, 79 CE, the volcano erupted, having a slightly predictable effect on the surrounding towns, which were buried in ash. Many of the inhabitants were killed from the heat wave during the eruption, and they were buried as well. While the Emperor (Claudius) did his best to help out the refugees, the buried city was abandoned and later forgotten until 1599, when ruins were discovered while a canal was being built. Since then, it's become one of our greatest resources for glimpsing life during the Principate. We can see (generally speaking) what the people were wearing when they died - while the bodies themselves have long since rotted away, they left impressions which are easily filled with plaster. We can see the food, the graffiti, the artwork, and the ruins, which are extraordinarily intact (Though that might not last too long if they continue to be as neglected as they are).

Pompeii is where we've gotten a huge amount of our knowledge of this period in the Roman Empire, and its state of preservation helps with that. Because of all of this, it's also a pretty big tourist draw, as you can imagine.

Hope that answers your question!