Describe the circumstances that led to the signing of the bond by Antonio and its consequences.

Antonio feels a very strong affection for his younger friend, Bassanio, and Bassanio is aware of this fact. Antonio is a wealthy merchant, so when Bassanio needs a loan in order to have to money to woo Portia, he naturally turns to Antonio.
Unfortunately, Antonio is extremely cash strapped at the moment. All his liquid assets are tied up in financing three merchant ships that are out to sea. When they come in with their cargos, Antonio will be flush with cash, rolling in money, but right now he has nothing. Yet he loves Bassanio so much he is willing to go into debt to help him marry Portia.
Antonio approaches the Jewish moneylender Shylock for a loan. The two have had dealings before. Antonio has been cruelly anti-Semitic to Shylock, and Shylock resents how he has been treated: insulted, hit, and mocked for being Jewish. He will only lend Antonio the money he needs if Antonio will sign a bizarre contract. The contract stipulates that if Antonio fails to repay the loan on time, Shylock can cut a pound of flesh from any part of Antonio's body. Antonio agrees, figuring that with three ships out to sea, at least one of them will return in time. Naturally, that doesn't happen, and, in consequence, Antonio has to face Shylock demanding his pound of flesh. This potentially means a death sentence for Antonio, as Shylock wants to cut the pound of flesh from Antonio's heart.