Here's my full cover of Barcelona by George Ezra. You'll find tutorials helping you to play this song further down this page!
Open D Tuning
The notes you need to tune to for open D are; D A D F# A D
It can be helpful to have a chromatic tuner, such as this one by TC Electronic, to get into this tuning.
The D chord can be played by just strumming the open strings (that's the idea of Open D!)
G and A major chords can be played with a flat first finger barring 5th and 7th frets.
The minor chords in this key can be played at 2nd, 4th and 9th frets either just by fretting string 7 at these frets, or with the chord shapes shown later in this video
Here's a lesson to help you get into Open D Tuning, and I highly advise watching this lesson if you are new to this!