The stages are the different steps or rounds in an event. You can see it as the structure of the event. You often decide which structure to choose based on the number of participants. For example, if you first have groups, which turn into an elimination draw, you then have 2 stages. For more information on stages: https://www.toernooi.nl/product/article.aspx?s=2&id=FB7ECADF-430D-43C3-B5D2-FA71BC94BE8A\