Sketches live inside projects. First select (or create) a project, then create a sketch within that project to start drawing.
Every sketch must belong to a project. If you don’t have a project yet, create one first from the Projects screen.
Once a project is selected, you’ll see the list of sketches for that project. From here you can create new sketches or search/open existing ones.
Use + create new sketch to start a fresh sketch inside the currently selected project.