Everything you draw is saved to this browser automatically, a moment after you stop working. The dot in the bottom left shows the current state. If you close the tab while something is still being written, the browser asks you to confirm first.
The toolbar stays hidden and slides in when the pointer moves near the bottom of the screen. The + button behaves the same way near the top right. Every tool shows its key under the icon, and \ hides all of it while you record.
For text, pick the text tool, click once, type, then click anywhere else to set it down.