Hi, Wendy. As Lucy said, you can be a member of more than one project here -- many of us are in several.
But project membership isn't required, and for most of us the first priority is adding our own family. You're still a Guest member of Wikitree. Please complete the steps to become a full member so you can participate fully. Then start adding your relatives. As you get familiar with the site, you'll have a better idea of how you want you engage with projects here.