Chords at their most basic level are a combination on notes that have a relation to each other. For the purpose of this lesson I will use the 1st, 3rd, & 5th notes of the major scale for our chord. Most often you see the 1st note of the triad in the root position. Inverted chords are simply useing some other note in the scale for the root. Example: Gmaj would normaly be G-B-D. Now just for fun you can take the third note of the scale "B"
and place it in the root postion. I do this on the 7th fret like so:
Instead of G being in the root now we have B anchoring the chord so low to high it is B-G-D-G. I also mute the two open strings. So now instead of haveing to bar a chord to play up the neck you have this option. The next cool thing you can do is make the third (B) a minor third which means slide your finger back one step. This changes your chord to a G minor.
Now you have B flat-G-D-G. So now that you know how to do this to a G chord you can apply this to all the major and minor chords you know.
Now, as to why the heck you would want to do this in the first place. When playing with friends who are playing in open chord position I always want to do something different than they are. It is boreing to me to have three guitars playing the same chord at the same fret in the same position. This gives you another trick to add to your bag and makes you a more interestion player no matter what the style.