There are daily and weekly Schnopsn tournaments. The respective top 20 (daily) or top 40 (weekly) players get Credits and points for the world ranking. The higher you score, the more points you get.
The winner of the weekly tournament receives 100 points, the winner of the daily 15.

But: score points expire after a while! At the end of the weekly tournament (usually Wednesday evening) every competitor in the world ranking loses 10% of points, and their score gets rounded down to the next whole number. For example, 91 points would decay to 80.
Therefore, to stay ahead in the world leaderboard, you have to keep competing. This guarantees that the top of the ranking is only made up of the very best players.
You need about 100 points or more to make it into the top 10, and 25-30 for the top 100.

The current world ranking is here.