Sorry for the noobe question but I cannot figure out how to make simple modifications to the default theme's home page. Something as simple as changing the furniture image to something else.

Furniture image can be change in the Bootstrap Slider plugin. Go to Admin panel -> Configuration -> Local Plugins -> Find slider and click Configure.

Thanks, but is there a tutorial on how to change ALL of the elements of the home page?

Well, all elemenents on homepage is a pretty imprecise term. You can modify the Index.cshtml file to change the order of the componenets and their appereance. You can also use the CSS to customize the styling of your store. If you ask more precise question, I will be able to answer you more directly.