Sessions you create are kept in Recents, which you can open from the left sidebar.
Sessions can be deleted from Recents by selecting a session and click Move to trash: Deleting a Workflow.
Sessions and projects shared with you
Recents is also where anything shared with you arrives. Shared sessions and projects do not appear in your sidebar on their own.
A green dot on Recents means something new has been shared with you.
Open Recents to see what it is. Each new item carries its own dot.
An item's dot stays until you open that item, not just until you open the list.
Once opened, a shared session stays in your Recents, and a shared project appears in your Recent Projects.
For how to share your own work, see Share your workflows.