In Act 1 Scene 2 of Shakespeare's The Merchant Of Venice, where are Portia and Nerissa and why are they there?

The location for Act 1, Scene 2 is Belmont, Portia's wealthy home. Portia and Nerissa discuss the way in which Portia's deceased father set up how she would find a husband--through a game of chance. Some directors show Portia and Nerissa in this scene walking around looking at the caskets created for the purpose of her father's game. These caskets are located at the home and are probably in a private room so suitors can make their decisions in peace. The reason they are walking around the room with the caskets is because there are six suitors ready to try their luck on Portia's father's game. Nerissa names each suitor for Portia so she can prepare her mind and heart for which one she may be able to accept as a husband. Unfortunately, she likes none of them. 

This scene is a vehicle for exposition so the audience can understand Portia's plight, her suitors, and part of her father's game. The full game of chance is demonstrated in further detail when the Moroccan plays the game in Act 2, Scene 7. This initial scene also has a foreshadowing in it because Nerissa reminds Portia of Bassanio whom she met once, and could be a good match. 

"Do you not remember, lady, in your father's time, a Venetian, a scholar and a soldier, that came hither in company of the Marquis of Montferrat? . . . He of all the men that ever my foolish eyes looked upon was the best deserving a fair lady" (I.ii.94-96, 98-99).

Nerissa refers to Bassanio and Portia happens to remember his name at her prompting. In the previous scene the audience first meets Bassanio who goes to his friend Antonio in an effort to get enough money to court Portia. This scene validates that Portia remembers him and gives the audience hope that the two will meet again and be able to marry if Bassanio can play her father's game correctly.