How to export an artboard from Sketch to Sparkle
Select the artboard in Sketch, from the “Plugin” menu choose “Sparkle”, then “Export Artboard(s) to Sparkle” then open Sparkle and choose Edit, then Paste (or press ⌘-V)
How to turn a button design into a working button
The button design in Sketch will transfer in Sparkle as a box and a label, or depending on your setup in Sketch as a group containing the box and label. You can turn either into a working button by select them, right clicking on the canvas and selecting “Convert To Button”, which will turn them into a fully functional button.
How to configure the artboard for optimal sizing in Sparkle
The artboard is scaled to the Sparkle canvas size, so if content is looking incorrectly sizes in Sparkle you can make the artboard wider or narrower for the scaling to be most effective.