Simply replace the unfilled areas such as "" and "[date]" with your information.
Dear [name of dean],
Thank you so much for taking time out of your busy schedule to meet with [me/us] on [date of meeting]. I enjoyed visiting your campus, and you provided me with a great deal of information about the college and the campus in general.
I believe that you have a very strong [department of interest] department, and [name of university] is certainly among my top choices. Should I choose to attend and am accepted at [name of university], I feel that I will receive a solid, well-rounded education.
Thank you again for spending so much time with us, and for all of the valuable information you provide.