For any competition, the playing handicap for that competition varies (for example, it's 95% for strokeplay not 90% and if playing foursomes it's 50% of the difference etc etc.) - All a player has to know on most days in normal competition is their gross scores. The player is NEVER responsible for calculating their nett score. As per the rules of golf that responsibility falls with the committee - or in club competitions more often than not, the computer. The player only has to record the correct gross score on each hole, and sign their card, as well as it being signed by a marker (or in these covid times, agreed by a marker after 9 holes and after 18)
Your handicap index is now key under WHS, as this determines your course handicap for the day. Again, you are not responsible for working this out correctly, the software has all the relevant data on the computer. However, it is handy, for singles ties for example, to know your shots. Your index is calculated from your best 8 rounds in the last 20.
Every single course in the world, should now have a table at the first tee, showing a list of handicap indexes. FInd your index, and it shows you your course handicap for the day.
Depending on the competition, 95% may be applied, again by the software, at the end of the round. This will happen for all club medals, stablefords, and opens.
A worked example below.
Joe Blogs Handicap Index - 18.5
Course handicap = Handicap Index x Course Rating/Standard course rating i.e. 113
Course handicap for Braids Whites (rating 121) will be 18.5 x (121/113) = 19.8 - this is rounded to 20 (so you can use this in the Sandy Rennie to work out shots)
Playing handicap = Course Handicap (unrounded) x Competition multiplier (100% for Matchplay individual, 95% for strokeplay)
Playing handicap = 19.8 x 0.95 = 18.8 - Rounded to 19 for the purposes of a strokeplay comp