Bassanio picks his Casket

It is pretty obvious that Portia wants to marry Bassanio. Bassanio is a young and not very frugal friend of Antonio's. He is a spendthrift who has wasted whatever inheritance he might have had. 

Having heard of the fortune that will belong to the man who marries Portia, he wants to borrow money from Antonio so that he can present himself as a financially suitable suitor to her. He has met Portia before and has read amorous looks in her glances, quite probably presenting himself as having greater means than he actually has, as is his habit. With the money he receives from Antonio, he hopes to recoup his losses with Portia's estate.

An ineffectual businessman, Bassanio proves himself a worthy suitor, correctly identifying the casket that contains Portia’s portrait.