If you would like to export content (a full page or a selection), you can use SilverBullet’s Export functionality triggered with ${widgets.commandButton "Export: Page Or Selection"}.
Exports are one-offs. If you are interested in sharing content onto other platforms and keeping things in sync, have a look at Share.
Out of the box SilverBullet ships with the following exporters:
The export infastructure as well as the above exporters are implemented in Space Lua here: ^Library/Std/Infrastructure/Export. If you would like to implement your own exporters, have a look at the built-in ones to understand how they work.