Change position width of sidebar and main content

Please could you help point me in the right direction of how to change the width and the position of the sidebar and main content. As seen here at my work-in-progress: https://www.geekette.co.uk the main body does not seem to work well, and the side bar is slightly too wide and too far to the right.

My aim is to make the page look just like this: https://www.silver-blade.net/fashion/index.html which is where I was playing with another blogging software.

I’ve been looking at the style.css for hours with no luck. Help?

Thanks!