Create a document by clicking on the "Create" button on the top left of the home page. Then click "Share" in the top right to make the document editable by a partner, and make it public to share with others with the url link.
Make different part studios with the plus sign in the bottom left, then add them together in an assembly. You can collaborate on any part of the document like a google doc.
You can animate any moving parts of the playground by creating an assembly, mating the parts with a mate, right clicking on the mate feature, and selecting "animate"