My layout shifts when I re-adjust my browser, how to I fix?

This is a Noob type of question, but I’M lost, everytime I re-adjust my Browser window my layout shifts with it, I want to make it not shift but instead stand still regardless of the browser window size. I’m using the Suffusion 3.9.6 theme, and I have it connected for editing in dreamweaver but can edit from wordpress also. Could use the help its bothering me.

(website is being developed on a local host, so I can’t link)