Oral Questions - these are taken in the first 55 minutes of the sitting day on Mondays; Tuesdays; Wednesdays; and Thursdays. Departments are allocated a part of each question time (the most important departments have the full period), on a five weekly rota. The rota can be accessed at http://www.parliament.the-stationery-office.co.uk/pa/cm/cmwib/order.htm. Members receive a short answer, but it is the supplementary which is of interest. The Minister will not know (but his advisers may have a guess) at what the supplementary will deal with. Most MPs dream of delivering a 'killer' supplementary, which floors the Minister and causes a crisis for the Government. Most Ministers enter the chamber prepared for most supplementaries - and an ability to deflect questions they'd rather not respond to on the spot.
The Questions appear on the Order Paper of the day http://www.publications.parliament.uk/pa/cm200708/cmagenda/ob80609.htm. More questions are submitted than would ever be answered in the time available. Therefore "the shuffle" takes place once the deadline for tabling (that is in the British sense, not the opposite American sense) has passed. The 25 questions selected at random (by computer) will be chosen for inclusion on the order paper, though rarely are they all called before time runs out. Oral questions not answered in the chamber receive a written answer. Since 1972, the ration for each Member has been a maximum of two oral questions on any one day; with the additional limitation that only one question may be put to one Minister on any day.
Written Questions - There are no limits to the number of questions that may be submitted for written answer. In due course (and some departments have better track records than others) the answer will come back, and is either published in full in Hansard - or an answer is given that details have "been placed in the Library of the House." Further details can be found at http://deposits.parliament.uk/
An example of Hansard - Written Questions can be found at http://www.publications.parliament.uk/pa/cm200708/cmhansrd/cm080606/index/80606-x.htm
An example of the 'Order Book' can be seen at http://www.publications.parliament.uk/pa/cm200708/cmordbk1/80605w01.htm
A detailed paper on PQs can be accessed at http://www.parliament.uk/documents/upload/P01.pdf