Hi Mark
Firstly, if you are just starting out with Toolset I would caution you that some time ago we stopped developing the Toolset Starter Theme, which is effectively deprecated in favour of themes such as those you can find on the recommended themes page.
It was decided that our resources could be better directed at ensuring compatibility with a number of themes that specialise in one thing—making themes—rather than trying to continuously improve our own theme. Use it for a while and you are like to run into limitations.
The main advantage of the theme is that it is fully-integrated with Layouts, meaning you can use Layouts to design the entire page, and not just the content area, with the header and footer coming from your theme as is the case with just about every other theme.
One of our team is a real fan of using Layouts this way, and maintains a theme himself which is very lightweight, and fully-integrated with Layouts. It is not officially supported, but is very well documented (in the code itself), so if you are an experienced developer you should be able to follow what it involved. See hidden link
As to the question itself, background images are a CSS property, but there is no provision for dynamically setting such CSS style rules.
However, it is easy enough to implement yourself.
Use a Visual Editor cell, which lets you add HTML to the page, and directly add style tags into the cell editor so that you can use shortcodes to generate dynamic CSS. Something like this:
<style type="text/css">
.some-div {
background-image: url("[wpv-post-featured-image output='url']");
}
</style>
Lastly, note that you are posting in the Community Forum for users of the free Types plugin. As a Toolset customer you can and should post in the Technical Support forum which we prioritise and where you should receive speedier service.