These open chords are played using at least one open (unfretted) string, shown in a guitar tab with the number "0".
The guitar tabs will show the different ways to play each of the chords. Strum all the strings of the chords together, leaving out any string without a note shown.
The open E minor chord is a good guitar chord to start with. It can be played using only a couple of fretted notes, and mostly uses open strings.
e|---------0----0----| B|---------0----0----| G|---------0----0----| D|----2----2----2----| A|----2---------2----| E|----0---------0----|
This chord also uses multiple open strings and a few fretted strings. The use of different fret locations will start helping your fingers stretch and quickly find the right frets of the chord.
e|--------------3----3----| B|---------0----3----0----| G|---------0----0----0----| D|----0----0---------0----| A|----2--------------2----| E|----3--------------3----|
e|---------0----0----| B|---------1----1----| G|----2----2----2----| D|----2---------2----| A|----0---------0----| E|-------------------|
e|---------2----2----| B|----3----3----3----| G|----2----2----2----| D|----0---------0----| A|-------------------| E|-------------------|