Tap on Select and select the file(s) you'd like to share to Showbie

At the bottom toolbar, tap on Share

Tap on Showbie here if you want to share your file as a .numbers file or tap on Export at the bottom of the new menu that pops up (to share as other file formats)

Select the file format that you'd like to export your work as

Tap on either Showbie or Copy to Showbie - the latter is better for larger files