Hey & welcome!  There are many different ways to voice any given chord.  If you see the symbol D5 all it means is to play a D & A note together somehow, somewhere on the guitar.  Adding the /A (slash A) means to play an A as the lowest or bass note of the power chord.  But just the chord symbol doesn't tell you exactly where or how to play it.

You need to know the specific voicing to use for the specific song you are learning. 

In the case of this song, that D5/A (actually a Dsus2/A) to E is played like this.

|--0--0--|--0----|
|--3--3--|--0----| 
|--2--3--|--1----| 
|--0--0--|--2----| 
|--0--0--|--2----|
|--------|--0----|  

I suggest looking for authentic notation versions like this one on musicnotes.com so you have some degree of authenticity about the transcription.

https://www.musicnotes.com/sheetmusic/mtd.asp?ppn=MN0051407

Hope that helps!