I got the message that I was invited to the alpha when I opened my client, but I just closed that window because my friends were waiting to play. Am I supposed to download something somewhere? How do I get started? Can't wait to help out :)
This board is the best place to discuss the client with Rioters and your fellow players, although it won't be our main source for feedback resolution. Look to the other tools, like the Submit Feedback button in the client, for that. As always, please follow the Universal Rules and keep content focused on appropriate topics for this board.