Now that the Marriage (same sex couples) Bill has passed all its stages in the House of Commons, the Bill is passed, as amended, up to the House of Lords.
In the Upper House, the Bill has to follow all the same stages that it passed in the Commons. These are:
1st Reading - where the Bill is literally read to the House - 21 May 2013
2nd Reading - the first time that debate on a Bill happens. In contrast to the House of Commons, the Lords, by convention, do not vote on a Bill at this stage. - 3 June 2013
Committee Stage - where the Bill will be scrutinised in detail
Report Stage - when the Bill, from committee, returns to the House and there is a 'report back', with peers able to table and vote on amendments
3rd Reading - the final stage of the Bill when a debate and vote takes place
Once the Bill has passed all these stages, Royal Assent will be given by Her Majesty The Queen and the Bill at that moment becomes the law of the land.
The full Bill, as amended by the Commons and presented to the House of Lords.
ADDENDUM
We now know that the Bill will continue on Tuesday 4 June and that Lord Dear, a peer who opposes the Bill, will then propose a motion "to decline to give the Bill a Second Reading", which is likely to be voted on.