What is the difference between the House of Commons and the House of Lords?
The major difference between the House of Commons and the House of Lords (I assume that you are talking about the Parliament of the United Kingdom) is that the House of Commons is a democratic body whereas the House of Lords is sort of a holdover from the days when Britain was less democratic.
The House of Commons is elected by popular vote of all Britons over the age of 18. The House of Lords is not elected in any manner whatsoever. It is made up of people who are either A) senior bishops of the Church of England or B) "peers" or nobility who are selected by the monarch.