Everyone starts at D rank with 0 points. Winning sets/matches causes you to gain points, losing sets/matches will cause you to lose points. How many you gain/lose depends on the rank of your opponent, based off of who wins:
-Opponent is of same rank or lower: +/- 1 point
-Opponent is 1 rank higher/lower: +/- 2 points
-Opponent is 2 ranks higher/lower: +/- 3 points
-Opponent is 3 ranks higher/lower: +/- 4 points
-Opponent is 5 ranks higher/lower: +/- 5 points
For example, let's say a D ranked player beats an A ranked player. The D rank player will gain 4 points, while the A rank player will lose 4. If in this scenario the A rank player won, they would gain one point, and the D rank player would lose 1 point. It is also done by set and not by game, ie
this best of 3 win only counts as 1 point for Spino and not 3.
There is a minimum amount of points needed to become a certain rank, noted next to each tier in the list above. Reaching that number of points will cause you to go up to that rank, but going below that number of points will cause you to go down in rank, obviously. You will also get an emblem if you reach each rank beyond D, and said emblems are displayed next to each rank above.