"I'm confused about the difference between Content Block elements and Content Page elements. What do each of them do?"
Content Blocks and Content Pages perform, essentially, the exact same role. They host content that can range from text, images, HTML, and so on. The key difference between them however is that Content Pages feature a clickable page title bar while Content Blocks don't.
Content Pages should be used when you want to create a new mobile webpage that users should be able to navigate to by clicking on a published page title bar that links to that page. This is commonly the element that sees the most use on most mobile web pages.
Content Blocks should be used when you want to display content on the site but do not want the user to have to click on a link to view that content. Content Blocks might be used on the homepage to display welcome text, or a custom icon-based navigation menu, Content Blocks are also great for nesting on another mobile webpage when they contain content that might change with some regularity, or, as a means of adding additional content to a Content Page that's already been built.