Login into your Google Drive, open Google Drive settings.
On the Settings popup, click "Manage Apps" from the left menu, then click "Connect more apps" from the top center area.
On the popup, type "Secured Signing" from the search box. The "Secured Signing App" should appear in the result list. Click "Connect" button to connect Secured Signing app with your Google Drive.
Once Secured Signing App connected, a connected popup should be shown.
Next: learn how to use Secured Signing App