In the installer's Administrator account step enter a username (3–40 characters: letters, digits, _, ., -), an email and a password (at least 8 characters). The password is stored with password_hash() and is never written in plain text anywhere.
Open https://your-domain/admin/. Failed attempts are counted: after 5 failures from one IP within 15 minutes, login is temporarily blocked. The session ID is regenerated on login.
In Administrator account you can change the username, email and password. The current password is required for any change.
Version 1.1.0 has no email-based reset. Way to recover: generate a new bcrypt hash with password_hash() and replace password_hash in the users table via phpMyAdmin. There are two roles, administrator and member (since 1.1.0). If another administrator exists, they can set you a new password in the Users section.