Note:you should buy SSL certificate from your hosting provider and ask them to install it for facebook website folder before install facebook template to the server. It's Facebook requirement for each app. Please follow this link to find more details.
1. Create New App
Visit https://developers.facebook.com find App tab and search option to Add a New App.
Then select Facebook Canvas Platform to get started
Skip a Quickstart.
Next type an App Name (This can be anything you want, the name you are going to call your tab would be a good choice), Select the Cetegory Apps for Pages and click Create App.
2. Configure your App
Please go to settings tab and add platforms: App On Facebook and Page Tab one by one.
Please refer to image below and read a description after it:
Secure Page Tab URL - https://yourwebsiteURL/ (you should type your website URL with https connection)
!Important! Make sure all your URLs end in /
Page Tab Name - Specify your tab name.
Page Tab Image - Upload the icon for your tab.
After you finish entering those fields click the Save Changes button.
In order to make you app live so that your visitors could see application you should enable it in App Review tab.