Each doubling of frequencies is divided into twelve somewhat evenly-spaced semitones. If you go up seven out of twelve (using index 0 for your initial frequency), that's essentially half way to the doubling of the frequency with a ratio of 3:2. E.g., if your starting frequency is 440, going up seven steps will give you a note with a frequency of 660.

Another way of dividing up the space between a frequency and it's doubling uses eight of the twelve semi-tone divisions . The eight notes form an 'OCTive'. The octive has a 1-based index for the starting frequency. You can see seven out of twelve highlighted notes in the dashboard circles . The eighth note has the same name as the first one as you complete the circle but it would either be double or half the frequency. Going up seven semi-tones using the twelve division 'chromatic' scale is the same as going up five steps in the more selective eight note octive scale.

Yes, the circle continues from 2n<->4n and 4n<->8n and n/2<->n and n/4<->n/8 etc. The boundaries are those of human hearing from about 20hz to 20khz.

The white keys on a piano are the key of C Major. The black keys are the 'accidental' notes--the five notes of the twelve division chromatic scale that are discarded when selecting the notes for the eight (7 + the 1st/8th note that is counted twice to complete the circle) note octive.