Literally, ‘to invert’ means to turn something upside down or on its head. Do you remember what triad chords are? The bottom note of a triad is called the ROOT. Inverted chords require rearranging the triad notes so that the root moves above the other notes. This is called the FIRST INVERSION.
Moving the two lower notes above is referred to as the SECOND INVERSION. The clip shows an example of a C major triad. They are shown here on a stave. The red note shows the position of the root each time.
Here they are again so that they can be played on a keyboard using chord 1 in C major each time. Often, the first inversion is called 1b and the second inversion is 1c. Therefore, the root position is 1a. The chords below show how to refer to them if playing a guitar.
The clip also shows that using inverted chords means that it is possible to move more smoothly from one chord to another. Look at the following link. One shows chords in root position and the other shows a few inverted chords.