Bottom line
This section spells out what "satisfactory participation" actually means for you. If you are in an SMCR unit you owe 48 IDT periods and up to 15 AT days a year; if you are an IMA you owe 48 IDT periods and up to 13 AT days a year. Just showing up is not enough: you also have to meet standards on appearance, fitness, body composition, attitude, and effort. The section also covers when a school commitment locks you into a Statement of Understanding (SOU), and the extra fitness bar you must clear to serve in a load-bearing ground combat arms unit.
What it means for you
Your participation requirement depends on your Training Pay Category. SMCR and IMA Marines both drill 48 periods a year, with a different cap on AT days. If you are in the IRR, your rules are in Chapter 8; Standby Reserve rules are in Chapter 9.
Two things often surprise Marines. First, attendance alone does not check the box. You can be at every drill and still fail to participate satisfactorily if you blow standards. Second, if you go to a formal school the Marine Corps may put you under an SOU, a contract that obligates you to keep drilling for one, two, or three years depending on how long the school was. If you want to serve in certain ground combat arms units, you also have to pass a PFT and CFT bar tied to that unit's criteria.