Open D tuning
The open D tuning is popular among guitar players who, for example, using a slide.
When you retune your guitar it’s important that you turn the tuning pegs in a direction that decrease the string tension and not the opposite.
To get the open D tuning on your guitar you should tune it like this: D A D F# A D.
These are some of the chords you could play in open position when using this particular tuning.
Moveable one finger shapes
All you have to do is to lay your fingers over the four highest strings and avoid playing on the two lowest strings. As the pictures illustrate the D chord could be played with all open strings.
The shapes are moveable, so if you move the finger two steps up the fretboard from G major you will get an A major and so on.
All common major chords in open D:
C: XX 10 10 10 10
This was an introduction about chords in open D tuning, see also open G tuning and drop C tuning