Block text is always surrounded by an invisible boundary called a container. You can connect text containers so that block text flows from one container to another. You can flow text among any number of text containers (including text in shapes). You can either connect existing text containers or create a new text container that flows from an existing one. You cannot flow to a different page.
Text overflows a container when there is more text than can fit into the container. When you edit text, an overflow handle (a small "+") appears at the lower right border of the container to show that there is overflowing text. Text flows from the back object to the front object. If you don't reorder the objects, text flows from the first drawn to the last drawn object.