Portia gives Bassanio the ring with a warning, and Bassanio accepts the ring with his own pledge. How is this contract or bond similar to and different from the one made in Venice?

If Bassanio loses the ring or gives it away, he will lose her love. At least she doesn't demand a pound of Bassanio's flesh. 

If Bassiano loses the ring or gives it away, he will lose her love. It is similar because both have something like a comitment or an agreement and the difference is that Portia’s contract is more about love and it’s pure, while the contract made in Venice was kinda non-sense if you look at it.