If your page in the Sitebuilder is redirecting to another website as soon as you click into it making you unable to edit the page content, this is due to some code you have added to the page (possibly code for linking to an affiliate website). The code includes a redirect which is activating in the Sitebuilder.
What you will need to do is remove the block of code from the page that you last added before the problem started. If the redirect is happening too quickly for the code to be removed, the only option is to re-create the page.
If the redirect is important, you should wait to implement it until you are sure the page is completed and will not need to be changed.