How do I play this on my guitar?
A side question, is there a reference site for checking music and tablature notation?
This is a tie, meaning that the initial D is held through the eighth note, the quarter note, and the first sixteenth note before the hammer-on to E. It appears that the reason it was written this way (i.e. two ties) was to give the rhythm along with the notes, as in standard notation the ties would be written in the same way.
The way this tie is written is really more of a general music notation practice than a tablature practice. Unfortunately, tablature is not really standardized in the way that traditional music notation is, as many tablature sources transcribe only string/fret combinations and leave the rhythm to be figured out by the performer.
As far as standard music notation, there are many websites that provide explanations of music notation symbols. I would start HERE, but a google of 'music notation reference' provides many decent results.