Your "Fullwidth Subpage" templates allows up to 6 content sections and the "Default Subpage" allows up to 4 sidebar sections in addition to 6 content sections. Each section can contain text, images, etc.

Content > Sections

Content - This is the main content block and supports the content/styles of the page content.

Background Color - This color allows you to set the background color of the section and should be a html hex value.  A good reference is http://www.w3schools.com/tags/ref_colorpicker.asp.

Background Image - This serves as the section background image.  This image should be 1,600px in width, while the height will depend on the amount of content in the section.  A recommended height would be between 600px and 1,200px (double for retina).

Dark Background - Selecting this checkbox displays the content in white color on top of the site default section background color or dark background image.  

Parallax Background - This option turns the Background Image into a parallax background that remains static as the user scrolls vertically.