Regarding Mics

I was looking to get myself a good mic and came across the mics from Hollyland Lark M2 and DJI.

I saw that both of them have 1 receiver and 2 transmitters.

Now I'm new to mics and have just a basic idea about them. So what I wanted to know was the purpose of 2 transmitters and the receiver. Now I know that the receiver is connected to the phone/camera that's you're recording with, but have no idea as to why there are 2 mics and how to use them?

And also what is mono and stereo channels and when to use either of them.

Please help.