Google is your friend: Be nice and visit him often. He can answer questions a lot more quickly than posting them here...
A very quick search
using your subject as the search term gave over 6 million results:
Google[
^]
The second link is an article on this very site!
Retrieve Mail From a POP3 Server Using C#[
^]
In future, please try to do at least basic research yourself, and not waste your time or ours.