The Parliament of Great Britain is the United Kingdom's main lawmaking body. It is divided into a House of Commons and a House of Lords. The House of Lords is now fairly irrelevant but it does some useful work revising legislation from the House of Commons.
The members of the House of Commons are sent by the town or district which they represent.
An interesting fact: the Queen is not allowed in the House of Commons except during the annual opening.
The House Of Lords
It's fairly pointless at the moment, and definitely undemocratic. It's members are called 'peers' and they are possibly the most unrepresentative bunch of people you'll find in the UK. Most of them are stinking rich, and some of them are peers simply because their parents were. However, the Lords is undergoing a good old 'spring clean' at the minute. Although it seems the reformation has slowed down somewhat, as the folks in the Commons just can't seem to agree on how many peers should be appointed and how many should be elected. It should not escape attention that Tony Blair kicked out most of the hereditary peers (the ones who inherited it from their parents) and then created more life peers than any other PM in history, thus stocking the Lords with his supporters. If the Lords is reformed, and all the peers are elected by the people, then it will have a democratic mandate, and might actually be able to do something other than temporarily delay legislation.
The House Of Commons
This house is the one with the real power. Members of the Commons vote on proposals, and if a majority vote is achieved, the proposals become law. Of course, what this means is that if the biggest party has a good majority in the House (as it does now) then it can effectively do whatever it wants (as it does now). As stated above, the MPs are elected by their constituents, and their purpose is to represent the people of that area but if the people want one thing, and the party wants another, the party usually wins... After all, you won't get a promotion if you disagree with your boss, now will you? However, British politics is far less party centric than those of the USA and "backbench rebellion" (i.e. MPs outside the Cabinet voting against legislation put forward by the government) is extremely common.