To enable two-factor authentication (if it's not already required by your organization) just go to omnystudio.com/account and click Enable under the Two-factor authentication (2FA) section.
On your next login to Omny Studio you will be prompted to setup 2FA. This requires the use of a Timed One-Time Password (TOTP) app.
To get started, you will be prompted to enable 2FA by scanning a QR code using the TOTP app of your choice:
If you have any issues scanning the QR code, enter the code displayed on-screen in the app your app of choice.
Once your app is linked, it will provide a 6-digit code for a limited amount of time. Enter that code and hit "Enable two-factor authentication" to login to your account.
When logging into Omny in future, you will be prompted to provide a time-based one-time password from your linked app.