If you click the little [-] button, you'll get an index for that page.
If you use the search bar at the top, https://doc.rust-lang.org/std/vec/struct.Vec.html?search=vec... will let you go right to the method. (In this case, you have to know that it's slice::len though)
Does that help?
EDIT: UX is hard! Glad people are discovering this. It's the same symbol HN uses, incidentally...