What is the basic format?

-The format of the UEFA Nations League will feature promotion and relegation and see the 55 European national teams divided into four leagues in accordance with UEFA’s national association coefficient rankings on 11 October 2017.
-League A will include the top-ranked sides and League D will include the lowest.
-Leagues A and B will consist of four groups of three teams
-League C will comprise one group of three teams and three groups of four sides
-League D will be formed by four groups of four teams
-The League Phase Draw for the UEFA Nations League will take place at the SwissTech Convention Centre in Lausanne on 24 January 2018.
-In each league, four group winners are promoted (or play in the Finals, see below) and four teams are relegated for the next competition to be played in 2020
-The overall UEFA Nations League rankings will determine the composition of the draw pots for the subsequent European Qualifiers
-In addition, the UEFA Nations League will provide teams with another chance to qualify for the UEFA EURO final tournament, with four sides qualifying through play-off matches which take place in March 2020 .

https://www.youtube.com/watch?v=yCXf63t7R8w

Qualifying for UEFA EURO 2020

Qualifying for UEFA EURO 2020 remains largely the same (with 24 finalists in all), although the European Qualifiers will now begin in the March after a major tournament instead of immediately in September (i.e. March 2019 in this case). No team will gain auomatic qualification as hosts (there are 13 host nations in all).

Qualifying group stage (20 teams qualify)
The teams will be split into ten groups of five or six, and the top two from each group will qualify for the final tournament, determining the first 20 places.

We explain how 16 teams will be whittled down to four as the final places for UEFA EURO 2020 are decided.
https://www.youtube.com/watch?v=slqy1rjQJaY
European Qualifiers play-offs explained
Play-offs (4 teams qualify)
The last four EURO places will be won through the European Qualifiers play-offs, which will be contested by the 16 UEFA Nations League group winners (i.e. the four group winners in each of the four divisions).

Each league will have a path of its own and each path will feature two single-leg semi-finals and one single-leg final. The winner of each path will win a ticket to UEFA EURO 2020.

If a UEFA Nations League group winner has already qualified via the European Qualifiers, then their spot will go to the next best-ranked team in their league. If a league does not have four teams to compete, the remaining slots are allocated to teams from another league, according to the overall UEFA Nations League rankings.

https://www.youtube.com/watch?v=HR4MIHqQyt0

What is this?

Went trough this quickly and its interesting at the very least. Just worried about the number of game they will do and how this could affect the club team. :(

Is it clubs or nations by the way?

55 European national teams

Thats from Emre initial post, lol.

So, they just released a video about it on the front page and I find it quite interesting, really sound like they are bringing the format used for club football into international football. I kind of like it personally, wonder what other think about it. :)

Obviously these won't be B teams, nor C teams, but probably teams composed of largely young players and those who fit in right tactics. So we can see literally anything, and I think it looks interesting. Good way to boost morale of younger players - they are young but already capped, if they make a mistake, screw it, it's a friendly.

@Croatian Well, from what I seem to understand, if you win it, you get a place in the next UEFA Euro or something like so it could happen to see a team work hard to win it all. Still, I agree its a good to give more experience to younger player and will permit weaker team to build their team over the year. :)