The play begins with Antonio (a merchant from Venice himself) with his friends Salerio and Solanio. Antonio is melancholy and his friends assume he's sad because he's worried because his ships - and fortunes - that are at sea. They try to cheer him up and then more friends, Bassanio, Lorenzo and Gratiano turn up. Gratiano, the loudest of the bunch, takes his turn to tell Antonio to get his act together and quit moping about, but this doesn't cheer him up either. The others leave, and Bassanio talks with Antonio.
Bassanio is a nice young Venetian gent. He's short on cash but he has a plan to go and try and woo Portia, a lovely young woman who inherited a fabulous fortune. Bassanio doesn't have enough money to present himself to Portia as a suitor, so he turns to his friend Antonio for money. Antonio would be happy to help him, but all his money is tied up in his ships that are at sea, so Antonio suggests that they use Antonio's good name to borrow some money to help out Bassanio. They turn to Shylock, a Jewish moneylender. Shylock hates Antonio for heaping anti-Semitic abuses on him. Shylock finally agrees to make the loan to Antonio interest free - but, if Antonio fails to pay the loan back on time, Shylock can claim a pound of Antonio's flesh as the penalty. As Antonio is confident his ships will come in, he takes Shylock's bond.
Over at Portia's house, her father left her in a strange predicament. She cannot choose a husband for herself. Instead, her father set up a system where anyone who wants to marry her has to pass a test by choosing between a gold, silver or lead box. Suitors come and try their luck at choosing the right casket. Eventually, Bassanio makes his way over to Portia's to try his luck in choosing the right chest. Word comes from Venice that Antonio's ships have sunk, and he will not be able to repay Shylock. Enraged that his daughter has eloped with a Christian, Shylock is hellbent on revenge and claiming his pound of flesh.
There's a trial to determine if the law will uphold Shylock's claim. You'll see whether the debt is forgiven or Shylock claims his pound of flesh and how it all works out in the end.
The first scene can seem hard to follow, but as the play goes forward, audiences find it increasingly easy to follow. Once you understand out what's going on with Portia, what's going on with Bassanio and what's going on with Shylock, the three stories collide nicely in the end.
This synopsis is deliberately brief as there are some surprises in the play which we think are more fun if they remain surprises.