Extreme Blog Makeover

...bloggy blog is going to be going through some changes. Now while I try and do these on my own (for the most part) I could REALLLLLLY use some help with something. I do not like my writing staying within the borders of my headers. Like, if you look at my sidebar, as well as my posts, they all line up directly underneath the header. How do I get my writing (posts) to spread across the page more, or I guess align on the left instead of the center????

Anyone????