4ths tuning is based on making all strings tuned one just 4th apart. This has the advantage (over the standard guitar tuning) that every fingering (provided no open strings are involved) is moveable across the fretboard, so your learning of fingerings is minimised.
As an example, this is what a G major scale looks like on a guitar tuned in E 4ths (the root notes, G, are red). Note the symmetry of the patterns repeating all over the fingerboard:
Notice how e.g. starting from any of the G notes with a given finger, you can play the exact same fingering pattern starting from different frets and different strings. If you have already been playing guitar for a while, you will realise how much simpler this is to memorise than with standard guitar tuning.
Look at this basic layout for one octave of G major, if you start from your first finger:
Starting from your second finger:
Starting from your fourth finger:
All of the notes of the G major scale based on a fixed position starting on the 3rd fret, which you can view as chaining the former fingerings:
Similarly, but based on the 2nd fret:
One of the things you may have started to notice is that all scales that derive from a major scale can be comfortably played using 3 notes per string.
As a final example, this is C Major all over the first twelve frets: