See the ITTF ranking document [here](https://www.ittf.com/wp-content/uploads/2021/01/ITTF-Table-Tennis-World-Ranking-Regulation-20220429-1.pdf).  The short answer is that you get a number of points for a win in an ITTF sanctioned event (an official tournament), and depending on the kind of event it awards more or less points. Page 8 shows the points; winning the Olympics gives you 2000 points, placing top 64 gives you 45 points.  Winning an International Event gives you 75 points.  

You take your top 8 finishes by points, and then everyone does the same, and sort by points - whomever has the most points in their top 8 events is #1, whomever is second most is #2, etc.  These ranking points last for a year, so if you win an Olympic event in 2024, you will have 2000 points (plus your next 7 finishes!) for the next year, but in summer of 2025 it will expire and those points will go away (and be replaced by your next highest finish).

A player might have:

1. Olympic win 7/28/2024 = 2000
2. Continental Cup win 8/19/2024 = 500
3. WTT Contender finalist 9/15/2024 = 280
4. International Event win 8/12/2024 = 75
5. International Event win 9/24/2024 = 75
6. International Event finalist 7/15/2024 = 55
7. International Event finalist 9/8/2024 = 55
8. Continental Championship R16 11/4/2024 = 45
9. Continental Championship R16 2/4/2025 = 45
10. WTT Champions R32 5/16/2025 = 15

On 6/1/2025, their ranking score would be 2000+500+280+75+75+55+55+45 = 3085 points (leaving off the last two since they only keep the top 8 scores).  On 8/1/2025, two events would fall of - the Olympics and the International Event finalist from 7/15 - so they'd have 500+280+75+75+55+45+45+15, or 1090 points, if they didn't have any additional results that scored in that time period.