The wiki page gives an overview of different tournament types: swiss-system, knockout/elimination, round-robins, and group-stages. These align pretty much exactly with the same meaning on BGA. The only real difference to note is that on BGA "round robin" tournaments usually mean all games are started simultaneously, whereas in sports, for obvious reasons, the games would be played consecutively.
If you go to the tournaments page - https://boardgamearena.com/tournamentlist - you can filter by game and tournament type. The main tournament page for each tournament tells you how many games will be played, how many players in each game, maximum/minimum sign-ups, start-date, length of games, etc. If it all looks like something you want to join in with, then you can click the button to register for the tournament.
If a person understands what tournament types mean in sports etc (as explained on that Wiki page link) I'm struggling to work out what makes BGA tournaments additionally confusing?