Its complicated, to iron things out, next season (16/17) its "off-line". It will be used but won't affect the desicion. They will just collect the data and see how it would have impacted things for research. In season 17/18 it will come "online".
The Gazzetta article says:
To be enforced when a goal happens and determine if there was offside or the ball wen out before, or something like that. Goal line tech is already in place (don't know if its also in EPL).
Straight reds and penalties. My interpretation is that video will help the ref give the straight red (or not) when a foul has already been called.
The article then says:
"It gets complicated when, in case there is an episode that calls for a review, the ball has not stopped. In the protocol there is the possibility to stop the play if the ball is in a "non-influencing" zone, or to just wait for a stop in play. There is also the option of "challenges", where the coach requests a video verification."