A project holds everything for one brand or campaign: one Swatch, your Yarn, and the Patterns you have built from them.
What a project is
A project is a plain folder on your computer. You can open it, copy it and back it up like any other folder. Nothing is hidden in a cloud account.
Several brands
You can keep as many projects as you like. Each has its own Swatch, so a post for one brand can never pick up the colours of another.
On the Projects screen
Each project is a card. Open its menu, or right-click it, to rename, duplicate, archive or delete it, or to choose its picture: one of its images, or a new one you upload. In Yarn you can also open an image and choose Use as project picture. Your model can set it too, with set_project_picture.