A very quick tutorial:
Create a map pool for each of the five modes in the game. Add as many or as few maps as you'd like.
Once your map pool is finished, add the rounds that appear in your tournament. Each round needs a name and the number of games within it.
Finally, choose a generate option to create a map list. You can have the app try to make one, or you can make one from scratch if desired. You can always edit the final result.
Once your map list is finished, you can export it as a discord message, or JSON file, or share it via URL.

More tips:
You can quickly create a graphic of your map pool to screenshot by clicking the 'Show Map Pool Graphic' button.
You can share your map pool with someone by sharing the URL provided in the Save or Share Map Pool button.
Once you've generated a map list, you can view how often a map/mode appears by clicking the stats button