Sailranks is a platform complementing esailing video games (providing the tools needed to registers scores, manage esailing clubs and plenty more)
To compete in a regatta, you need to be already registered in an esailing game such as Virtual Regatta Inshore
To enter a regatta, you need to get in contact directly with the race organizer, either via their discord, facebook, web page etc. The race organiser is the one that will add you to Sailranks.
If there is no indication available from the race organizer, best is to engage with some of the participants via the in-game chat to get you started.