If you wish to change the site structure or decided to exclude some pages, you need to remember about setting redirects for those urls, because previous link addresses will not be valid (in search results on Google) and this will result in a '404 Page not found'!
If the page does not exist on the new website, '404 Page' - is, of course, the correct action. But if the page still exists, but in a different location, you can add the so called 301 redirect to avoid this 404 error.
This chapter will show you how to add these redirects in your TYPO3 installation version 9.
NOTE: Redirects Extension is automatically installed on new TYPO3 version 9 - but it is available just for admin users! If you (as an editor), don't have access to this option, you can contact your TYPO3 supplier and ask them to add you the right to work with redirect extension.
Go to the 'Site management' module in the TYPO3 menu on the left side (9.1):
To add the new redirect record, you just need to click blue button 'Create new redirect' shown on the screenshot above (9.1), and then you will need to filled in next fields (9.2): choose the 'Source Domain' (1) from the dropdown menu, enter the 'Source Path' (2) - this is the 'Old path', that should be redirected to the new 'Target' page (3) - this is the new goal address for the redirected page, which can be chosen from the page-tree structure of the existing site or by adding external url (when you click the 'link icon' at the end of this field (3) - then new window appears, where you can choose the page in the same way as building regular link). The last step is to choose 'Status Code HTTP Header' (4) which identifies what kind of header will be sent to the browser.
There are several 'HTTP Status' codes you can use (9.3):
After the creation of the first redirect, the redirects will be listed as shown below, and you will be able to create new redirects by clicking the plus icon (9.4).