We answer "listo" for some request for us and it had completed the request.
for example:
can you check your speakers? answer: listo
could you turn on your camera? answer: listo
and we answer 'Entiendo' when someone explain you something and you catch the idea or understand.
for example:
you need to clean your room if you want to go out. answer: Entiendo
your computer is very hot because the fan is not working. answer: Entiendo
do you understand this explication? answer: Entiendo