I haven't seen the programme, but I'll give this a go: 1. Congress is the collective term for the two houses - the senate is one and the House of Representatives is the other. Both houses need to vote to pass a bill for it to become law - similar to the commons and the lords in this country 2. The Whip's job is to get senators to vote in a particular way. Usually they will vote for what their party believes in, but the whip may try and persuade senators from the other party to vote for their bill. The US system differs from ours in that the President might not have a majority in one or both of the houses, so might have to get the other party to vote for their bills in order to get anything passed. 3. To pass a bill means to get both houses to pass a majority vote on something, so that it becomes law. I presume this usually takes bloody ages, with much wrangling and compromise.
Some of this is gleaned from West Wing, so might be TV politics rather than actual!