Green AF Box vs. Yellow Exposure Circle?

[looopson]

Can anyone explain how the yellow exposure circle works in DJI Go app? I understand the green box is for auto-focus because it says "AF" underneath it, but I don't understand what the yellow exposure circle is for. It seems you can click it around the screen, just like the green box. What does it do? Thank you.

 

[Egika]

I measures the exposure in the selected part of the picture.
If you have uneven light distribution over your frame you can select which part the AE should consider neutral

 

[Robert Mitchell]

Similar to spot metering, it only measures the light in the circle area instead of the whole frame.