Hummingbird,

Books have been written about alternate tunings. Guitarists use alternate tunings to get a "different" sound from standard tuning. If you use alternate tunings you have to use alternate fingerings.

Here are a few to get you started. Notes are bass to treble, left to right.

Dropped D tuning
DADGBE

Used primarily in the key of D. Many standard chords can be used. But you might want to use some alternate fingerings.

Chords as shown here are bass to treble, top to bottom. The number indicates which fret you press down on that string.

G chord

5
5
0
0
0(3)
3

Parentheses indicate alternate fingering.

Em chord

2
2
2
0
0
0

Open G tuning

DGDGBD

Makes a G chord without any fingering. A barre across all 6 strings at the fifth fret is C, at the seventh fret is a D.

Sort of C chord

0
0
2
0
1
0

Sort of D7th chord

0
2
0
2
1
0

Open D tuning

DADF#AD

Gives you a D chord when all strings are open. G at fifth fret, A at seventh fret. (Similar to open G)

Sort of G chord

0
2
0
1
0
0

Sort of A7th chord

2
0
2
1
0
0

Both open tunings are commonly used to play "bottle neck" style. Any cylindrica object can be placed across the strings and slid up and down the fret board while picking the strings. Very unusual sounds are capable. Also some very beautiful sounds in the right hands.

Last, but not least, in this lesson.

DADGAD tuning
DADGAD

Base Chord (sort of D)

0
0
0
2
0
0

Alternate chord

0
3
2
0
0
0

This last tuning I learned as "D Modal" tuning. It was described to me as a cross between a major and a minor chord. Very eerie at times. I play some "old timey" banjo sounding tunes on it (the sister tuning was common among Appalacian banjo players). I understand it is quite popular in Celtic music as well.

Hummingbird, this should be enough to keep you confused and in wonder for some time. (If you understand any of what I have described).

Enjoy the music.