Chords are usually played (or described) in root position, e.g. for a-c-e you don't play the bass-string E.
But if you want to play an inversion (Am46) or the change of 4th in the bass line: a-e-a-e then the E-string has to be picked too.
The same constellation you have in C major or c minor and all other chords.
If you play the open strings of your guitar tuned E-A-D-g-b-e you have almost an Em chord: Em = egb ... Now you have in your open strings already E (6) ....g-b-e. (3-2-1 these are the numbers of the open strings) A and D are not elements of the Em triad and can only be changed by augmentation (pressing 2 fingers in the 2nd fret of and shorting the string length of the A and D string: So we get another b and another e). If you continue this method you will find numerous chord pattern for the same triad or tetrad. (There are no rules - except you play i.g. the a minor or the E major chord with your fingers 2,3,4 and move them as barré chords with the index finger from fret to fret - you can also do so with the G major chord, C major, D7, A7, e minor or the diminished chords.
here are some examples of simplified chords where you might develop the tones that are played:
Writing them down, notating in a staff system and comparing with the keyboard pattern will help you to understand the principle and to transpose them fret by fret (a halftone ) higher.
Root position and inverted chords A chord is in root position if its root is the lowest note. This is sometimes known as the parent chord of its inversions.For example, the root of a C-major triad is C, so a C-major triad will be in root position if C is the lowest note and its third and fifth (E and G, respectively) are above it – or, on occasion, don't sound at all.
more information you'll find here: