Can I use Site Studio 'Elements' to create content?

Yes. You can use Elements on the layout canvas to create content but it is not recommended.

You can use elements to create content but it is not recommend. This is because the design of the page will be entirely coupled with the content. This will make it difficult to make changes to your website layout without changing every page. A better approach is to use Components. These will allow you to create decouple the design and layout of your website from the content. Making wholesale changes to the layout will only require changes to your components. Form more information, see Creating a component layout.

Enabling elements for the creation of content (not recommended)

As of version 5.6.0 elements are disabled by default from use on content entity layout canvases. 

This can be set on a field by field basis within the layout canvas field settings.