These chord forms are movable chords, in other words, they can be made and used on any fret of your uke.
Once you understand how they work, you will also understand that if you make the chord at the nut (tuner) end of your uke, playing the lowest note(s) as an open
string(s)...this chart contains all the popular open chord forms. The "R" is VERY important, as it tells you what chord you are making.
The "R" stands for "root note" and names the chord.