Authenticator apps like Google Authenticator, Authy, Microsoft Authenticator and 1Password all enrol an account the same way: they scan a QR code containing an otpauth:// URI. That URI holds the account label, the shared secret key (in Base32), and a few parameters — the algorithm, the number of digits, and the refresh period.
This generator assembles that URI for you. Pick TOTP (time-based, the usual choice) or HOTP (counter-based), enter the issuer and account name that should appear in the app, paste the Base32 secret, and adjust the digits or period only if your system needs non-standard values. The defaults — SHA1, 6 digits, 30 seconds — match what almost every service uses.
Everything happens in your browser. The secret is never sent anywhere, but it is encoded directly into the finished QR code, so treat the downloaded image like a password: don't email it around or leave it on a shared screen.