Sending A Variable Over The Network

So, i have created a game, where you can create a server on 1 pc, and join it from another, and then both controll your own player. But, its a co-op, you need to find 12 things, if player 1 picks something up, how can I send this Int to player 2? So that it'll say, Player 1 Collected a Note, x/12 Notes Collected.Preferably in C#

Its probably an easy answer, but i have no idea. "I saw another post on it, but the answer was unclear"