First there is the House of Lords and they do many things. They improve and write new laws. They check the work of the government by asking questions and debating. Also they provide a group of experts to discuss issues. The House of Lords consists of Life Peers, Bishops, Archbishops, Hereditary Peers and Law Lords.
The House of Commons is very similar to the House of Lords but there are some differences between them. First of all, they write the laws and send them to the House of Lords to review them. Unlike the Lords, the Members of Parliament (M.Ps) are elected by the people of the U.K. M.Ps represent a big group of people like Congressmen in the Untied States. An M.P. can talk about things that concern people in debates in the House of Commons.
(P.S. If you are wondering, I'm still not answering yesterday's question about Westminster Abbey. If you know the answer you can post it in the comments section)