There's 16 groups split into four leagues - Leagues A, B, C and D each with four groups (A1, A2, A3, A4, B1 etc). All of the UEFA teams were allocated into the leagues according to their standings in the UEFA rankings for this first tournament but there'll be promotion and relegation for subsequent tournaments.
They play each other home and away, at the end the four group winners in League A will play two single Semi Finals at neutral venues then there's a Final and Third/Fourth Place Play Off.
The bottom side in each group (and the worst 3rd placed side in League C) is relegated to the next league down and the group winners in Leagues B, C and D all get promoted.
The seedings for the qualifying groups for the Euros will be done according to the final standings in the groups too - League A teams will be seeded 1-12, League B 13 - 24, League C 25 - 39 and League D 40 - 55.
Basically just a way to make friendlies more meaningful and make UEFA more money from the TV rights.
Given that he's spent the last few weeks doing everything other than wearing a Real Madrid shirt with his name on the back in public to try and get a move to Spain it'd be interesting to see if he gave up on his dream move or go anyway and wait for Conte's inevitable sacking.