Once and for all, how to center your blogger posts:

Click to enlarge.

The world wide web had no answers for me. So I found my own and am instead offering them to the world wide web. I feel like gloating; I couldn't tell you the first thing about html 10 minutes ago and yet here we are, viewing a beautifully centered and cleaned-up layout. To access the pictured screen go to Design (in your navbar) --> Edit HTML, and scroll down until you spot this section. You can tinker with the various numbers to fit your preferences, but these are what worked to get my posts centered.

Take THAT, blogspot.

ADDENDUM:  As you see my webpage now, the outer-wrapper "padding" = 30px. Changing this value to 30px moved everything 30 pixels to the right and down 30 pixels from the bottom of the navbar. It did not change how the different sections relate to one another.