Just Built a Theme

So I am very new at building themes at the moment and now that I have sort of figured it out, I was wondering how do I code for having my “middle section” expand as I add posts… I don’t know if that makes sense and I don’t know if its a php issue (like with the footer or something) or a CSS/XHTML issue. look at my site https://albeyo.net/blog and look at the very bottom, you see my links are now not on the sidebar. Please help? (Please go easy and be more helpful than critical, I’m so new to wp theme building!!!!)