You are about to enter tool mode. While using a tool, your mouse cursor will appear as a crosshair to denote how badass you are. As you hover over things on the page that can be modified, a border will appear.
The tool you select will remain active indefinitely, even if you use it to modify several things on the page. To exit tool mode and return to the regular editor, press escape at any time.
The select tool lets you select objects on the page and edit them. Instead of deleting something and creating a new one, you can use the select tool to change the options you used.
Click on something you've added to the page and an edit menu will appear.