Theory you can hear
Music theory is descriptive, not prescriptive: it documents the patterns people's playing has produced. You could rediscover them by playing alone — it just takes longer. On the instrument the patterns are shapes: the major scale is one shape in every key on a neck, the pentatonic is that shape with two notes removed, a triad is three of its notes, and the chords of a key are triads stacked on each of its degrees — the nesting the whole curriculum is built on.
The course's blocks below draw each of those on the instrument and let you tap them; the figure above is the same viewer, with every set in the row. And theory is only known once it is heard, so each block ends in an exercise: hear it, play it back.
On the ukulele: four strings, high-G tuning, the whole neck. Every set in the row above is drawn at every fret and key; a tap plays it.