You can turn off the microphone in the Settings (upper right corner)

It helps when you practice pronounciation. Without the mic you could be pronouncing the words all wrong. But if you listen closely and repeat the words for yourself, you will learn even without the microphone.

I don't use a microphone and I am gaining verbal proficiency by saying them without one... In fact it is even better without one because if you did the lessons with one, you would be practicing something you could do anyway instead of gaining written proficiency... Make sure you learn the alphabet though and your sounds first, and you will be awesome...