TOTP stands for Time-based One-Time Password. It is a method for generating temporary passwords that can be used for authentication. TOTP passwords are generated every 30 seconds and are only valid for a short period of time. A corresponding smartphone app is usually used for this purpose.
An indexed secret is a numbered character string of which several different digits are queried by the system during the login process. The requested characters are entered without spaces, without the "&" character and without a number from the first line of the table in the displayed form field.
Example based on the illustration: if the digits 4 and 10 are queried, the entry is: zm