Bassanio asks Antonio for a loan in order to pursue Portia from Belmont.
I'm afraid not.However, you may borrow money on behalf of my security.
ANTONIO'S
My dearest friend Antonio, may you lend me some money?
Bassanio and Shylock form a bond. If it is failed to be repaid within three months, Shylock shall take a pound of Antonio's flesh.
Rest assured; all will be well.
If the bond is not repaid within three months, I shall take a pound of Antonio's flesh!
SHYLOCK'S
 After the death of Portia's father, he leaves behind threecaskets of gold, silver, and lead. Whoever chooses the correct one shall become Portia's lover. However, all her suitors are deemed unsatisfactory.
Oh my, Portia! All thy suitors have failed!
Bassanio arrives in Belmont and chooses the lead casket. In doing so, he wins Portia. His friend Graziano asks for Portia's maid Nerissa to be his wife. Portia gives her ring to Bassanio, making him promise never to give it to another. 
News arrives that Antonio's ships have been lost at sea, and he is now bankrupt. They are also told Shylock insists on the fulfillment of his bond and has had Antonio arrested. Bassanio and Graziano leave in haste to help Antonio. Portia and Nerissa follow afterward, disguised as lawyers. 
We must head back to Venice and save my dear friend Antonio!
In the court in Venice, Shylock demands his pound of flesh. The Duke, presiding over the court, seeks legal advice from the lawyer "Balthazar," who is Portia in disguise. Antonio's death is only prevented as Balthazar explains that Shylock's contract does not entitle him to any blood. 
The bond is for flesh and not for a single drop of blood!