You have picked a massive scene to summarise. Act IV scene 1 is the famous court scene where Shylock goes head to head against Portia, arguing that he has every right to claim his "bond" from Antonio. The Duke of Venice himself asks Shylock to show mercy, but Shylock remains resolute, saying that he hates Antonio and doesn't need further reason than this. Bassanio, with his new-found wealth, offers twice the amount of the debt to Shylock, but again he refuses. Shylock reminds the Duke of the importance of upholding the law for the reputation of Venice.
The Duke says he will make no final ruling until a famous expert in the law arrives who will rule on the issue. Nerissa arrives, dressed as a man, pretending to be a messenger from Bellario. The letter says Bellario has sent a young learned lawyer to help the Duke. This learned lawyer is actually Portia in disguise. She establishes the circumstances of what is going on by questioning Antonio and Shylock. She as well asks for mercy, which Shylock refuses. Much to Shylock's delight, she insists that the law must be upheld in this case. Portia gives Shylock one last offer of three times the amount of debt to let Antonio live, but again he rejects any form of mercy. Antonio prepares himself for death.
However, Portia then reveals that although he can take his pound of flesh, the original bargain did not mention any blood. Therefore, if Shylock sheds any blood he will be arrested for trying to kill a Venetian. Shylock tries to backtrack, asking for the money instead, but Portia says that he has refused this offer and now must take his flesh. Now trying to leave, Shylock is stopped by Portia, who reveals a law that says that anyone who has plotted to kill someone loses their wealth and their life is left at the discretion of the Duke. The Duke grants Shylock his life but confiscates his wealth.
Shylock wants to be killed at this stage, but Antonio steps in and asks that the wealth be kept in a trust for Jessica and Lorenzo, and that Shylock must convert to Christianity. Shylock has no choice in this and leaves a bitter and twisted individual. Portia and Nerissa leave, but not after being given by Bassanio and Gratiano respectively their marriage rings that they had sworn never to part with.