I'm having some trouble with the same theme, Suburbia. I can get it to do everything I want except put widgets in the sidebar.
As for answering your question, I may be able to help a little. If you go to your THEMES page, you should see the SUBURBIA theme at the top with a partial description and then READ MORE ABOUT SUBURBIA. If you haven't already done this, reading this may help you. It did me.
So far I have several "pretend" posts set up, so I can work with layout and see what it looks like. When you include a photo in your post, make sure you click to make it the FEATURED photo and that way it will show up at the very top of your post, just like the demo shows.
To make the top two large, like the demo, you have to do a sticky post on the posts you want to feature. I had to research all this stuff, cause I didn't know how to do it. To do a sticky post, when you are making the post, or editing the post, on the right upper corner is the option Visibility: Public. Click "edit" next to that, then options will appear. Click the box next to "Stick this post to the front page". It will put that post at the top of your homepage and make the photo large like the demo.
Hope that helps.