Here’s a visual guide to the states and tooltips. A cell can be in one of three states: closed (>), open (⌄), and pinned (▾). The pinned state is “sticky open”: the cell remains open even if the cell loses focus. Pinning is typically used to show readers code when publishing, but it can also be useful if you are frequently editing a cell and want it to remain open.
You can click anywhere in the left margin to open and focus a cell. (You can also use Alt-Shift-Down or Option-Tab ⌥⇥ on mac OS to navigate focus with the keyboard.)
If you click on the caret (>) instead of the gray part of the left margin, you’ll also pin the cell.
When the cell is open, the caret rotates down (⌄), a left border appears connecting the cell’s output and its source code, and the cell’s left margin turns gray. You can click the caret or hit Ctrl-Shift-P ⌃⇧P to toggle between open (⌄) and pinned (▾).
When a cell is open (and not pinned, ⌄), clicking on the left margin or hitting Escape ⎋ closes it:
But when a cell is pinned, it will remain open; clicking on the left margin of a pinned cell doesn’t close it—it just refocuses it.
You can also close a pinned cell that’s not focused by clicking on its caret:
The play button (▷) is in the bottom-right of the editor. Clicking it or hitting Shift-Return ⇧↩︎ commits any changes to the code and reruns the cell.
The play button also indicates the “dirty” state of the cell; it turns blue (︎) when you have uncommitted changes.