Hi Reena,
The university will most likely prompt you about the interview well in advance. However, I have also heard that sometimes, you only get 2 days to prepare.
There are a few common types of interviews universities take-
A recorded video interview - you will receive a pre-recorded set of questions on your screen, and you'll be allowed to take some seconds to prepare before answering each question
Informal QnA sessions - several students will be called at the same time, and the mediator will judge you based on your preparedness, presentation, and communication skills
One on one - this is the regular kind of interview that gets conducted over a telephone or Skype
Some universities also conduct group sessions and case studies as part of their interview process