Here are the main points I understood:

The only way you can be sure your mental map accurately represents reality is by allowing a reality-controlled process to draw your mental map.

A sheep-activated pebble-tosser is a reality-controlled process that makes accurate bucket numbers.

The human eye is a reality-controlled process that makes accurate visual cortex images.

Natural human patterns of thought like essentialism and magical thinking are NOT reality-controlled processes and they don't draw accurate mental maps.

Each part of your mental map is called a "belief". The parts of your mental map that portray reality accurately are called "true beliefs".

Q: How do you know there is such a thing as "reality", and your mental map isn't all there is? A: Because sometimes your mental map leads you to make confident predictions, and they still get violated, and the prediction-violating thingy deserves its own name: reality.