To add a call-to-action button to your Page, follow these steps:
1. Login to Facebook – Visit your Page and click the “Create Call-to-Action” button (as shown below).
2. Select the CTA and URL - Select the most appropriate call-to-action and enter the URL you want people to visit. Click the “Next” button” (as shown below).
3. Select the destination for mobile users – On the next screen select a destination for iOS or Android users.