Please don't expect everything to work perfectly. However I'm very open to any suggestions and feedback! See below for how to submit feedback.
Click on the shortcut in the toolbar to the right of the hotbar and then use the tool to select an area. Shift-clicking will allow you to enter text that will be displayed underneath the selection.
There a two per-user settings that allow both the size and the duration of the selection box to be adjusted.
- There is no keyboard shortcut to open the tool (a shortcut will be added in the next version)
Please create an issue here for bug reports and/or feature requests.