The State Opening of Parliament takes place each year and is the most colourful event in the official parliamentary calendar.
On this day, the reigning monarch arrives at the Palace of Westminster and after being dressed in the Parliament Robe of State and the Imperial State Crown his or her majesty will be seated and then say:
My Lords, pray be seated
The monarch’s messenger, known as Black Rod (from the expanded name Gentleman Usher of the Black Rod) will turn and begin to head towards the House of Commons. The doors to the room will be ceremonially closed before he reaches the entrance to symbolise that the house can act without the presence of the monarch or their representative.
Black Rod will knock three times on the door and say:
[Mr or Madam] Speaker, The [King or Queen] commands this honourable House to attend [His or Her] Majesty immediately in the House of Peers
The members of the house will then be asked by the speaker to follow Black Rod to the House of Lords. Once here the monarch gives a speech and formally opens parliament for the given year.
Similar traditions and openings are seen throughout the realms under the reigning monarch.
Video: State Opening of Parliament – 2013 – BBC (Only viewable within the United Kingdom)
Further Reading: State Opening of Parliament on the Official Website of the British Monarchy