x means don't play that string at all. o means play that string open.
The dashes are just spacers, presumably some kind of timing device (there are 36 'zones' in a 'bar'). And although this would be a good idea, I don't think it's employed here, as the guitar starts at the very beginning of the bar - the chords shown don't!
So, basically, it means very little! Presumably, you've listened to the song. That will most likely give far more clues than blindly following what someone has tabbed. Seriously!
That apart, if you're learning piano, it's somewaht counter-productive to try to translate guitar tab (especially as you don't play guitar!). You will be better off finding proper piano music, and learning to translate that. Honest!