The double elimination format is very similar to the single elimination format, with a simple twist: like the name suggests, you have to lose twice before being eliminated instead of just once.
Double elimination is divided into two brackets: Winners / Upper bracket - teams that still haven't lost a single match Losers / Lower bracket - teams that have lost one match. Losing a match in the lower bracket will result in being eliminated from the tournament.
In the example above, all teams start in the upper bracket. The losers of games #1 and #2 will proceed to the lower bracket, and the loser of that game (#3) is eliminated from the event.
The grand finals of the event is held between the winner of the upper bracket VS the winner of the lower bracket - however, there is one detail to it.
Considering the team coming from the upper finals hasn't lost a match yet, typically, that team has an advantage. This could either be, for example, starting a best of 5 with a 1-0 score or simply something like choosing more maps, sides and starting drafts.
Some organizers also use what is known as "Bracket reset" (game #7 in the example), which is having the finals being played twice in case the team from the winners bracket loses the first match in order to keep the core of double elimination bracket - losing twice in order to be eliminated from the event.
This is determined by the tournament organizer hosting the event and may vary from genre to genre.