Creating a new topic on the forum is as easy as navigating to the board where you want to post, then using the "New Topic" button at the top right or bottom right of the posts list.
The General Contractor demo uses the widget method for the logo; there is a text widget in the "Logo" position with the code that was used. For that demo, the logo was all code, no images at all; just an ionicon for the hammer, and custom HTML for the text.
As for the other images on the site, all sample image placeholders are located in the "images" folder at the root of the site (next to wp-content, wp-includes, etc). Background images will be defined in the theme options under either the Specific tab, or Main->Layout. Most other images are widgets, you can find out what positions they are in by adding ?tp=3 to the end of your site URL (Like This
). Once you find the individual widgets, you'll be able to see the names of the image files, and that will let you find them in the images folder for reference of each size.