I wasn't even aware of this new competition until fairly recently and have only just decided to look into what it involves, so I had a look on the UEFA website.
In a 'nutshell' there are 55 teams involved and these have been split into four groups (A to D) of four leagues (1 to 4). Some groups/leagues will have 3 teams per league and some (those with the lower-ranked teams) will have 4 teams per league with the 'league' matches being played in September, October and November.
The competition will then see the top team in each league within group 'A' (four teams in total) compete in two semi-finals, a third/fourth place play-off, and a final, in June 2019. There will also be a promotion/relegation system between the four groups (A to D) at the end of the season which will determine the leagues for the subsequent season, the next one of which will be in 2020/21, not 2019/20 which is when the exisitng European Championships competition will be held.
The 'ins and outs' of the competition is explained in a 60-page downloadable PDF 'booklet', and I have attached a copy below, if anybody fancies reading it.
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