To organize chords, we can utilize a guitar chord numbering system. We name a particular chord, the one chord (also known as the tonic). Once a chord is named the one (I), it's alphabetical from there. So, if A is the one chord, D is the four chord (IV), & E is the five chord (V). If A is 1, D is 4, & E is 5.
Guitar chord numbering is a great way to keep track of relationships between chords. It is important to memorize (move information to pure knowledge) the relationships between chords.
And, definitely memorize the relationships, starting with C, G, D, A, & E (the main 'guitar keys'). This knowledge plus a capo gets us functional in all keys.
Tonics like to move to Subdominants. Subdominants like to move to Dominants. Dominants like to go to Tonics. When chords follow this progression ( I to IV to V to I), this is considered progressive harmony (regressive being the reverse).
We left off the viio chord because we rarely use them. The tones of the diminished chord are the 3rd, 5th, and 7th of the Dominant 7 chord. We can use the V7 chord in place of the viio.