Blocs pages are broken up into 3 areas. The top global area, the dynamic content area and the bottom global area.
The Global Areas
Global areas are content sections that appear on all of the pages within your Blocs document. Blocs placed within them will be visible across your entire site. The global areas are typically used for your navigation (top global area) and footer (bottom global area). They can also be hidden/disabled from any page via the page settings.
The Dynamic Area
The dynamic area is the section that is unique to each page, it’s generally the area used for main content that is unique to a page.
It’s very common for new Blocs users to accidentally place all of their Blocs into the top Global area and then find it confusing when these Blocs show on other pages. A quick way to check if a Bloc is global is via the layer tree. Blocs in the global areas of a page have a blue stripe on the left side in the layer tree.