So, as far as I can tell the event is play event levels, receive items that you trade.
The first set of maps, available from the 18th give you items that can be traded for fire and earth levelling and maybe evolution items

The second, available from the 20th give you items that can be traded for wind and water items

The third, from the 22nd give you light and dark

Throughout all of this you can get gifts too, which can be traded for Sonya (maybe only from the start of the third set of maps?), medals, and gold evolution statues. Also for gold present boxes.

The gold present boxes can be traded for 5* limit break material that is dependent on show, not class. The shows available are urara, kiniro, A-channel and new game. You can only trade 2 of these, though I'm not sure if its 2 for each show, or 2 in total.

It's should all be fairly obvious once the event starts, but at least they do seem to be giving out 5* limit break materials in events.

All of the worthwhile stuff seems to be limited to presents, and it doesn't look like you'll be able to exchange the other items for presents.