The Ranking hierarchy is summarised here - why not check out the Tournaments section of the website to find out more.

2021 10 15 Bronze Hierarchy

Your ranking is based on three-monthly snapshots taken on 1st September, 1st December, 1st March and 1st June of each year.  Your ranking can improve at any time once you have accumulated the appropriate number of Master Points, but the level at which you're allowed to participate will only change on those dates.  You can check your ranking on the MEMPAD site shortly after each three-monthly date, and the currently valid searchable list is posted on the home page.