The D&D Adventurers League is an organized play campaign in which players all around the world play the same D&D adventures. In contrast to home games of D&D, in which pretty much anything goes, in organized play, players all expect to play the same adventure , regardless of who is DMing and where they are playing.
Just as the name implies, the D&D Adventurers League is a league game, in which everyone plays by the same rules, whether they always play in the same place or play all over the world. Characters within the League are portable, so a player who visits another area or moves there or who plays in an online game expects to be able to play his or her character there without having to make any modifications and without having to learn any local rules.
Even players, who never wind up playing anywhere else or with any other DMs expect to have approximately the same experience as players in other locations, so when they discuss their games in social media and other places, they are discussing a common experience in which they faced the same challenges and had the same chances to earn the same rewards.
Adventurers League characters are divided into 4 different Tiers.
Tier 1 : characters of 1st-4th level
Tier 2 : characters of 5th-10th level
Tier 3 : characters of 11th -16th level
Tier 4 : character of 17th-20th level
Adventure League modules are designed for specific tiers of play. In order to play in a module your character must be of the intended tier e.g. to play in a Tier 2 module, your character must be of 5th-10th level. If your character falls outside of the intended level range, they cannot be played in that module and you will have to play a different character, or play a different module of the appropriate tier.
Basically you play a several oneshots with the same character with different groups.
Your character will gain +1 level, after every game-session.
How treasure works please see the links to the google-docs in the first post of this thread.
hope that helped