Hi heeseung,
You have just installed the WHMCS template, not the WordPress theme.
Please install the WordPress theme to follow the steps from the provided documentation to get feel like as our live demo http://preview.themeforest.net/item/virtusky-responsive-web-hosting-and-whmcs-wordpress-theme/full_screen_preview/20499450?_ga=2.223881435.1328434217.1529640523-453348612.1529391384
Please Note: Mainly, our item is a WordPress Theme and we have just provided WHMCS template for FREE of cost with our theme by customizing WHMCS default six template’s header, footer, and color based on our theme to use separately.
In this case, you need to use both WordPress Theme and WHMCS templates separately. WordPress Theme to show/represent your products/services and WHMCS template for billing like as our demo.
Moreover, you need to link up all of your products/services (buy now link) to your WHMCS.
Furthermore, you could use the WHMCS Bridge Plugin to integrate the WHMCS into the WordPress to follow this video tutorial https://www.youtube.com/watch?v=tmQ3apTdrMA&t=0s&index=3&list=PLbmIKrgYlRbrak6Ymxl2Qkp83gsNhGRYp
Best Regards,
ThemeLooks Support Team