Repetition

I would like to ask if there is a formula to trace or maybe it would highlight names that are being repeated in the excel?i have 10,000 names on it and i want to highlight or want to trace which names are there already or being repeated.
i have already a thousands of list and my friend forwarded me again another list of names,I'm pretty sure that some of the names are being repeated.
I'm basically a beginner and it would be very helpful to teach me each step to solve this kind of problem.
thanks..