Mahjong Helper calls each complete game of Mahjong a "Match". ie. Four Rounds - East, South, West, and North - in non-Japanese Mahjong, each Round has each player be East at least once, for a minimum of 16 games (in European or Hong Kong Mahjong), or 8 games (in Japanese Mahjong, where the game could end after the South Round if someone has 30,000 points or more).
You can have a record of multiple matches, but only one is considered "Active" at a time.
To mark a match as "Active", select the radio-button to its left.
Press the "Add" button to create a new match. It will inherit the same settings as the previously "Active" match (Ruleset, Initial Score, Players, etc.), but start at game #1.
Tapping on the arrow will let you set the parameters for the match, such as the Ruleset, Initial and Limit scores, whether Bonus tiles (Flowers & Seasons) are used, whether East passes on draws, etc.
Delete a match by swiping left to reveal a 'delete' button, and pressing it.
Note that you cannot delete a match if it is the only one in the list - instead, add a new match first, then delete the old one if you want to get rid of it.