Learning Golf Strokes

How to calculate Stableford Points?
I’m a 25 handicap and I’ve recently joined a golf club and have played in a couple of medals. So far the club have calculated my points for me but I should learn how to.
I understand that a 6 handicap for instance would add increase the par by one for Stroke Index holes 1-6 and for an 18 it would be adding one to SI 1-18.
I just get confused as to what the fromula would be for a handicap higher than 18. Can anyone help?
Thanks
Let’s say you have a handicap of 25, which is 7 more than 18. In that case, you will get a two stroke handicap on each of the 7 most difficult holes, and one stroke on each of the other holes. If your handicap is 36, you get two strokes on every hole.
Learn How To Play Golf Strokes and Rules