Remember this advice isn't official. There is no guarantee it will reflect your experience because university applications can change between years. Check the official Cambridge and Oxford websites for more accurate information on this year's application format and the required tests.
Also, someone else's experience may not reflect your own. Most interviews are more like conversations than tests and like, any conversation, they are quite interactive.
2 interviews in the morning, then an essay in the afternoon on the same day.
I was sent an article to read a couple of weeks before the interview, and was asked questions about it in my subject interview. This gave me time to fully process the information and brainstorm possible questions that they could ask (they ended up not asking any of the questions I thought they would, but as I was so familiar with the contents of the article, I was able to give an answer that I was happy with).
During this interview, I was shown a graph and initially misinterpreted the data, but once I had realised my mistake I corrected myself. It was terrifying! The interviewers pushed me until I could no longer think of alternative arguments, but this is exactly what they want to do and you should expect to reach a point where you feel out of your depth.
In my general interview I was shown another brief article and asked to expand on points on it. In this interview, they also referred to my personal statement and asked me to expand on points that I had made.
I stayed over at Emmanuel, but my dad came up with me and spent the time after my interviews and before my exam with me. This really calmed me down so that I was in a more stable position before I started my exam. I would recommend bringing a parent if you can!