I had a great time talking with my research supervisor. They were very thorough about the work we are going to do. I was really excited to start! I worked there for a semester.
The interview went very smoothly and I was given thorough explanations of the tasks I will be performing. They also gave me a lot of info on the culture of the lab I was applying to.
Meeting with a professor, postdoc or professors are rather informal. Sometimes there are UROP postings online that give details about what the lab is looking for, but there is definitely merit to approaching professors personally or via email.