First you will want to determine your IP address.
Google will display your IP Address at this link:
https://www.google.ca/search?q=my+ip
Create a file named .htaccess with the CPanel File Manager in the public_html folder or Add-on Domain folder if it does not already exist.
At top of the .htaccess file add the code below.
Replace 123.456.789 with your IP address.
order deny,allow deny from all allow from 123.456.789