Setting Callout text and url
As you can see in demo there is Callout text and link button in every page template. And actually the same Front Page Widgets also.
Page templates in Kalervo theme
You can set them when you edit page under Page Attribute.
Callout in theme customize
Next thing you want to do is set Callout text and url. You can do that under Appearance >> Customize >> Front Page Callout.
That wasn’t hard, was it.