Projects are a useful way to organize your work into separate spaces or even do versioning or forking for all your projects.
When you first log into Tenderly and start using it, you'll be prompted to create your first project(s). After that, you can select your project(s) from the dropdown or create new ones:
If you're a part of an Organization, you'll be able to access all projects that belong to it and they'll be visible in the dropdown. Alternatively, you can click the View All button.