When I was applying I had a few phone conversations which were almost like interviews where they asked about my interests and experiences, but they were informal and then formal interviews and visits were organised. I wouldn't beat yourself up too much about it, I hadn't done much in the way of lab work and so I didn't always know what they were going on about but I was just honest and they seemed OK with that. So i wouldn't worry too much that you were unsure about things, one supervisor told me that as long as you know the basic theory then any technique can be taught. He was more interested in motivation etc.