Ladder
You can play ladder games just by going fight! -> similar player.
If you win you will earn ladder points. If you lose you will lose some ladder points. You get more points for beating higher ranked people. You lose less points the higher the enemy is ranked. So it isn't so bad to lose to someone of a higher rank than you but if you manage to beat them you get a lot of points.
The people with the highest ladder points at the end of the week will win gold and the points will be reset for the next week.
All ladder games are against people of a similar skill level so really anyone can win the weekly gold.
You must be within 100 points constructed rating of someone for the ladder game to count. And both of you must have a rank uncertainty less than 170. If you beat someone of higher rank than you you will gain more ladder points than if you beat someone of a lower rank than you. If you lose to someone of lower rank than you you will lose more ladder points than if you lose to someone of higher rank. Each game you play with the same person in the same week counts for less ladder points. You can't have negative ladder points.