To customize your layout and theme go to Design tab.
You can choose between a Full Screen layout and a Pop Up.
You can further choose how the elements on the page would be aligned on the Theme below.
In the end you can add your own background by clicking on Add Background Image
You can upload your own image as well as add your company name. In the middle field you can add a link to click, so when the user clicks on the background it takes him/her to your website.