Now that the zeroheight plugin is installed in Sketch, you can upload your Sketch files by choosing an option in the plugin:

• Upload selected frames uploads only the selected artboards and master symbols in a particular Sketch file, as well as document colors, shared layer styles and shared text styles in that file.
• Upload all frames uploads all the artboards, and master symbols in a particular Sketch file, as well as document colors, shared layer styles and shared text styles in that file.

You can keep working while your upload is in progress, and you will be notified once the upload is complete.