Drop D Tuning
This song is in drop D tuning. In drop D tuning the low E string is tuned down one whole step to D. This enables the guitarist to play power chords with a single finger.
In these measures, the beginning chords are the same in the slide. All you have to do is form a standard D chord, but just play it as described below. Then, all you have to do is slide to where you actually play the D chord. Use your 3rd finger for the notes on the third frets. End the second measure by using your 3rd and/or
4th finger to barre the fifth and then the third frets.