TOTP follows time
TOTP derives its moving value from time. Its generator can display a countdown because the time window has a predictable end.
HOTP follows a counter
HOTP uses a counter. The generator and verifier need to stay sufficiently synchronized for the service’s rules.
Use the type your service configured
These types are not interchangeable switches for a live account. Read the setup link or the service’s documentation before choosing a generator.
Which tool should you open?
Use the main code generator for TOTP. Use the HOTP generator when you have a counter-based setup and know its counter.