First, we will talk about major 7th chords. Specifically a drop 2 E major 7th chord with the root on the 5th string. We'll start with the basic voicing of root, 5th, 7th, 3rd, 5th. We'll then remove the pinky, giving us root, 5th, 7th, 9th, 5th.
By removing the pinky we free up that finger to play the embellishments. In these examples we are catering to what the pinky can grab easily.
In this case, the common extensions are the 13th (1st string), 3rd (2nd string), and the octave (3rd string). Since our pinky is free, it can easily grab these extensions giving us a few options.
These added notes are just half of what makes the R&B sound we're looking for, the other half is the phrasing ideas we'll be using. Specifically two in this tutorial. The first idea is an eighth note idea, raking the chord with a sweep motion, followed by some hammer-ons and staccato notes to end. Pay close attention to the video to get this phrasing right. The second idea gives the notes a fluttery effect using sixteenth note triplet hammer-on pull-offs.