TYPO3 v9 has reached its end-of-life September 30th, 2021 and is not maintained by the community anymore. Looking for a stable version? Use the version switch on the top left.
You can order Extended Long Term Support (ELTS) here: TYPO3 ELTS.
After the basic installation procedure is complete, TYPO3 will be working and the most appropriate settings will have been made for you. You will get redirected to the Backend and can log in with your administrator account.
If you want to make changes to your installation settings at a later date, use the "Admin Tools" in the backend. You can find more information in the section "In-Depth Installation", subsection "TYPO3 System Management".