What does it mean to increase the exposure of the camera by one stop? For example: Does changing the aperture from 8 to 5.6 count as an increase of one stop?

Increasing one stop doubles the exposure. When a single item changes, such as doubling the time and doubling the sensitivity, the aperture value is related to the "diameter" of the light. When the light area doubles, the light The diameter is square root 2 = 1.4 times. When the aperture is single-variable, the aperture value is divided by 1.4 for each additional stop. 8 = 5.6 × 1.4, so the example you gave is an additional stop.