Hi Henry,
Thanks for reaching us and welcome to X 
I will try to give you a short overview to get started with your website.
We offer two products. X Theme and Pro Theme.
You are running X, at the moment the main differences between these themes are that X Theme offers Demo Content Page which can be loaded via WP Admin Dashboard > X and Pro offers the super powerful header and footer builder.
We will be launching soon a solution to replace the demo content functionality on PRO which will bring a lot of more power for both themes.
Now back to your website.
When starting a website with X, I tend to look over the demos we offer and load a demo if I feel any of those demos can be a good starting point to my design. to load the demo you can go as I mentioned to Wp Admin Dashboard > X
Standard demos offer the home page only with placeholder instead of content. While the expanded demos offer a full website with content.
In case you decide to load a demo which has Slider Revolution, Remember to Install and activate the plugin on our Addons Section on Wp Admin Dashboard > X
Instead of using WP Customizer we suggest using X > Theme Options - The Theme Options is where you will set the general styling of your website, button colors, link colors, font type-face…Header style etc…
X Offer 4 Stacks, which also can be selected on Theme Options, each stack has it’s own style and some different functionalities
If you install a demo or not I recommend starting with Theme Options to set the general style of the website.
Once you do that you can use Cornerstone to build your pages.
Cornerstone offers Classic Elements and the new V2 Elements. I would suggest you starting with the classic elements since they are less customizable and will require less time learning at this point, of course I also suggest exploring the new elements with time 
You can find a lot of videos about X and Cornerstone on YouTube and on our Knowledge Base:
Hope it helps and let us know if you need further assistance.
Thanks