This part of the test is sometimes called the 'long turn'. It will last for three or four minutes, though you will not need to talk for all of this time.
Your examiner will ask you to speak for one or two minutes on a particular topic. The examiner does not choose the topic, but instead gives you a task card. The task card tells you what you should speak about, and some ideas connected with the topic, and also one aspect of the topic that you will be asked to explain.