On the day of your operation you will have the opportunity to ask questions. You will meet a physiotherapist and your anaesthetist who will explain what happens when you have an anaesthetic and answer any questions you might have.
You will also meet your surgeon who will discuss the indications, benefits and risks of you surgery. The knee undergoing surgery will be marked and you will be asked to sign a consent form.
You will be asked to change into a theatre gown and you may be asked to wear compression stockings, these help reduce the risk of developing a blood clot. With leg surgery these are not usually worn on the leg being operated on, but the nurses preparing you for your operation will tell you if and how you need to wear them. The operation can take between 1-3 hours.
To understand more about how knee replacement surgery is performed check out this animation on the NHS website (knee replacement). You will also find other useful information about why people have knee replacement surgery and some of the risks of such surgery.