The dead space above your footer is coming from the WP Review plugin. It’s best to contact the plugin author to learn how to remove the margin of that part.
Regarding the in your sections, edit each of your sections’ padding. By default, each section has a 45px top and 45px bottom padding. Set them to 0 for no padding. For more details about the Section and also Row and Columns, please read our documentation at https://theme.co/apex/forum/t/cornerstone-content-builder-sections-rows-columns/11445.
In case you decide to modify the section’s defaults, just know that you can set default option value of any V2 element. For more details, please read our Template Manager documentation.
More tutorials are available in our Knowledge Base and also our Youtube Channel.
Hope that helps.