For those still not understanding modes, here's another video lesson.
Playing in modes is all about playing from a different position in the scale whilst playing in the key of the root note.
Simply learn the modal patterns of the major scale - start the major scale on the E string from your root note which is the 1st position of the scale, then learn the continuing scale from the second position which will be the Dorian position and continue onwards, the 3rd position is phrygian, 4th Lydian, 5th Mixolydian, 6th Aeolian, 7th Locrian.
To play in a mode, you have to have a chord of the root or key you are playing in (or a chord in that key), and then take that modal pattern scale shape down to the root note and continue to play that scale position, you are now playing in a mode. But as has been said before, learn the modal patterns on each position of the scale and then go on to playing modes.
Here's the video lesson: