What are some good textbooks and online resources for learning about geophysics? That is, physics, as it relates to the earth's geology, shape, and internal structure.
I also strongly suggest the courses available on the coursera platform under the category "Energy & Earth Sciences" here.
There are two universally loved geophysics texts : Turcotte and Shubert and Stein and Wyessesion. Both are upper division/lower graduate level texts. Fowler is great if you do not have a strong mathematical background (multivariate calculus). Beyond that, it might be difficult to get a a good understanding without an Introductory physics course, and a few semesters of calculus. A good way to learn about geophysics, is in fact, just learning about physics and mathematics in general. Hopefully this stack exchange will also become a good resource.
Geophysics has many flavors to it. Prof Claerbout's site has a lot of free stuff which are a good introduction to one part of it.