Before a Popup can be added to a page, it must first be added to the website as a whole within the Popup Manager (See: Adding a Popup).
Go into the Page Content Editor of the Page you would like to add the Popup to.
Within the main Content Editor field, click where you would like the Popup to appear, then click on the Popup Button in the toolbar
Fill in the information on the small form that appears: Here you can enter the Text that will link to your Popup when clicked, and underneath that, select the Popup Title for the Popup you want to display.
Click the Green OK button and you will see a small snippet of code inserted where you clicked your cursor in step 3:
Once you have finished adding the rest of your content, click the Save Page button and you should see the result if you view the live page:
and you will see a small snippet of code inserted where you clicked your cursor in step 3:
and you should see the result if you view the live page: