In short, two nobles meet on the street during carnival in Italy. Montesor convinces Fortunado to go down into the crypt to see a special Amontillado cask of wine. He plans to murder him there because Fortunado has insulted him somehow. He tricks him into a tunnel and closes him in brick by brick, suffocating him.
Anytime that you read a summary, keep it mind that only the sequence of events is given. When reading Poe, there is always so much more to examine. For instance, the irony of what the unreliable narrator says is an important element to consider.
The first place you should always search is enotes reference section. They have lots of teachers and professional people writing for them. The link I provided is an excellent link here at enotes, and it will summarize the story and provide other helpful information.