The first chords every guitarist learns are open chords, which use a combination of fretted and open (unfretted) strings to produce rich, resonant tones. The open A major chord is a great starting point: place your index, middle, and ring fingers in a diagonal line across the 2nd fret of the D, G, and B strings respectively, then strum from the A (5th) string down, muting or skipping the low E string. Its minor counterpart, A minor, only changes one note — the index finger moves from the D string up to the 1st fret of the B string, flattening the third to a C note. That same one-note principle shows up across nearly every minor comparison: switching A major to A minor lowers the third; switching D major to D minor lowers the third on the high E string.
Two other foundational chords are C major and D major. The open C uses a stretched shape: ring finger on the 3rd fret of the A string, middle on the 2nd fret of the D string, and index on the 1st fret of the B string, with the G and high E strings ringing open. The open D chord is more compact — index on the 2nd fret of the G string, ring on the 3rd fret of the B string, and middle on the 2nd fret of the high E string — and uses the open D string itself as the root note. For both, strumming only the top four or five strings keeps the bass clean and avoids muddy open strings.
The E family gives players two of the easiest shapes on the guitar. E major places three fingers on the 1st fret of the G string and the 2nd frets of the A and D strings, and is one of the most resonant open chords because you can strum all six strings. E minor is even simpler, requiring only two fingers on the 2nd frets of the A and D strings. The simplified open F major introduces a small barre for the index finger across the 1st frets of the B and high E strings, plus two more fingers on the 2nd and 3rd frets of the G and D strings; the full barre version is more common at intermediate levels. Finally, the open G major chord is played with one finger each on the 2nd fret of the A string, the 3rd fret of the low E, and the 3rd fret of the high E, with the option to add the pinky on the 3rd fret of the B string.