So there is an extra two measures on top of the measure 58. What does that mean?
The one says "2da volta" means "second repeat". You play the given bars in the second repeat while playing the main variant (of the top staff, presumably) otherwise.
The "Ossia" means "Other": optionally, you can play the small variant instead of the main variant below it.
It simply means the second time you play the right hand slightly differently, sort of arpeggiated. 'Volta' means time or occasion.
'Ossia' is just an alternative part, to be chosen instead of the original under it. Usually an easier option, but ossia doesn't literally mean easier!