Purchase your favorite team stickers in CS:GO or from the Steam Community Market. A portion of the proceeds from sticker sales go directly to the teams competing in the Katowice 2015 CS:GO Championship.

Not only do they show support for your favorite teams on your favorite item, the team stickers also serve as game pieces for the Pickā€™Em Challenge, the CS:GO tournament prediction game.
Pick'Em Challenge Trophy
Pick'Em Challenge Trophies are badges that are displayed on your CS:GO avatar and on your Steam profile. There are a total of 100 points to score and a Bronze, Silver, or Gold Pick'Em Challenge Trophy will be awarded for scoring 25, 50, or 75 points, respectively.
Compete with your friends
In addition to winning a trophy you can compete with your friends on the Pick'Em Friends Leaderboard. Each day of the event provides an opportunity to score points for correct picks and you get a free point each day just for playing.
How to play
Your goal is to score as many points as possible by correctly picking the winning teams as the tournament progresses.

To make a pick during any stage of the tournament, you must own an unused sticker for the team you choose. You can get stickers by purchasing Katowice 2015 team stickers (in game) or from the Steam Community Market.

A single team sticker is sufficient for picking that team multiple times throughout the event.

Using a team sticker to make a pick will lock the sticker for the day. It will not be usable or tradable until the next day. Undoing a pick will not unlock the sticker. It will still be unusable and untradable until the event day is complete. Once the event day is complete, locked stickers will unlock and be usable and tradable.
Group Stage
Pick the 8 teams that will advance to the Quarterfinals. Each correct pick is worth 4 points.
Pick the 4 teams that will advance to the semifinals. Each correct pick is worth 8 points.
Pick the 2 teams that will advance to the grand finals. Each correct pick is worth 10 points.
Grand Final
Pick the Grand Final Champion. A correct pick is worth 12 points.

On each day you can earn an additional point just for playing. Trophies will be awarded after the tournament is complete.
Photo of Spodek Arena courtesy of WhiskeySix.