I probably wrote this in a previous topic, but basically peel the skin with a paring knife, and start slicing off the outer rind, dip in sea salt and eat. It's eaten like a green mango, and if you know Filipinos, they love sour or tart food, so santol rind, green mango, etc. is a good snack.
Once you reach the seeds, you can suck the pulp off, hence the English name, "Lolly fruit". It's kind of like mangosteen, but not cottony. You don't want to eat the seeds, but it won't kill you, at least lethally. Lol. It's quite common for parents to scold their children, because they sucked the juicy pulp from the seeds and ended up swallowing the seed. They then have bad constipation. That is kind of the thing you find in the rural provinces. The city children lose out on that "learning" experience.