Inversions are just chords that have their notes stacked in any order OTHER than having the root on the bottom.
At the very beginning, Scott likes to show and teach the chords in what is called "root position" meaning the root of the chord is the lowest note. That way you can "stack" the notes up from the bottom and then add another for the 4 note chords like the 7ths.
I want students to understand that the 7th chords are just an "addition" to the regular old major and minor chords. The downside to that is that you need to stretch to every other note all the way up, which often gives people physical hand-stretching fits once you need to put that 4th note on top.
In the real world, however, piano players quite often use something called an inversion where you take the same notes of some chord but you simply stack them up differently with something OTHER than the root on the bottom.
So instead of playing (for example) a C7 chord in root position like this - C, E, G, Bb - you might decide to put the C on top and play it like this - E, G, Bb, C (the same four notes, just stacked in a different order).
Or you might play it with the G as the lowest note: G, Bb, C, E. Again - the same four notes, just a different order.
That's all there really is to know about inversions. Just a chord that is being played with its notes in any order OTHER than root position (with the root on the bottom).