How do you get exp. share in Pokemon fire red?

Exit to the right of fuchsia city and there will be a building go in then go up the stairs and one of the professor's aide's will be there you have to a least 50 pokemon captured to get the exp share
Once you have gotten data on 50 pokemon in your pokedex, go to fuschia city and exit through the Eastern path. In the little police hut there will be some stairs, go up and claim your reward from Prof.Oak's aide!