The admin user has the ultimate power on your Moodle site. This user can do anything on the site, including creating other users. When you enter the details for this user, keep them in a safe place! The fields in red in the following screenshot are required. All others are optional:
Tip
Oh no! I forgot the password to my Admin user!
Don't panic! There are ways to deal with the loss of your admin user's password. You can still get it back, if you can get to the Moodle database. The frequently asked questions page on the Moodle website will tell you more: https://docs.moodle.org/28/en/Administration_FAQ#I_have_forgotten_the_admin_password
After filling in the required details for the admin user, scroll down and save your work. The install routine will advance to the next step.