You may wish to review  Open Chords, and Building Major & Minor Chords
before continuing with this lesson.

I wasn't in the room when they decided what open chords would look like, but I do have a system which allows you to figure them out on your own.  To do this you must know the notes of the chord (root, third, and fifth) and have a working knowledge of the notes in First Position.

STEP 1:  Identify the lowest root on the fretboard

STEP 2:  Go to the next higher string.  Leave the string unfingered if the open string is a chord tone (root, third, or fifth).  If it is not, place a left hand finger on the first chord tone  as you ascend the music alphabet.

STEP 3:  Repeat STEP 2 for each remaining string

For Example:

Build a C Major

STEP 1:  The lowest C in First Position is on the 5th string in the third fret.  Place your third finger on this note.

STEP 2:  The next higher string is the D, which is not a chord tone.  Proceed up the music alphabet to E, which is a chord tone.  Place your second finger on this note (4th string, second fret).

STEP 3:  The next higher string is G, which is a chord tone.  Leave this string unfingered.

The next higher string is B, which is not a chord tone.  Proceed up the music alphabet to C, which is a chord tone.  Place your first finger on this note (2nd string, first fret).

The next higher string is E, which is a chord tone.  Leave this string unfingered.

A few final thoughts regarding this method;

1)  Strings which are lower than the string on which the root is found are not intended to be played.  The root will be the lowest note of the chord.

2)  This method works well for finding Major, Minor, Dominant 7, and Major 7 chords.

3)  There are a few chords which cannot be reasonably constructed using this method