Aligning the whole theme to the left

This is a pretty simple question: I’m working with a modified version of Kubrick, which is a centered theme. I basically just want to un-center it so it sits on the left side of the page. I don’t know loads about CSS, but I’m learning, and slowly but surely catching on. I’ve looked over the code of a couple themes that are aligned to the left, but I can’t figure out what I should even be looking for– if it’s the margins or “float” or what, and where they should be defined.

I appreciate any help– if you can’t suggest an exact solution, but can still point me in the general direction, I can probably figure it out. Thanks!