Download and double-click the Finch.sketchplugin file and let Sketch automatically install the plugin for you.
You can also manually copy the plugin file to your Sketch Plugins folder.
You can export your global styles by selecting Plugins -> Finch -> Export Styles from the Sketch top menu bar. This will open Finch app and prompt you to choose the target project.
You can also similarly export your defined document colors by selecting Plugins -> Finch -> Export Document Colors from the top menu bar. This action will also require you to specify the target project in Finch app.