In each of these, the bounding box is a button, which you get by clicking the plus at the left, then choosing "button". To see a button's action and its hover effect, click "Preview" (upper right).
When you select a button or an image, the function buttons that appear above it include a link button, which opens a set of link-related options. Keep in mind, though, that the thing you want to link to must exist before you can link to it. That seems obvious, but it caught me a couple of times.
If you select more than one item, the "Group elements" button appears; if you select a group, the "Ungroup elements" button appears. Items in a group all move together. If you want to edit something in a group, first ungroup.