Part 83: Quantum Toast adds additional commentary.
As I understand it, either House can introduce a bill, but both Houses have to agree on it before it can pass into law. Which can mean it spends a while bouncing back-and-forth, getting rephrased and revised until they settle on something both accept. (It's not totally symmetrical, Lords can sometimes be overruled and has a bunch of restrictions that Commons doesn't, but I think that's the gist of it.)
post opportunity time! From an insiders perspective, does the House of Lords actually do anything?
So I guess a big part of their job seems to be to stop the House of Commons doing things?