mongodb - How to do spatial search using mongodb queries?

Question

I am trying to use spatial search in my android app. I am new to mongodb and spatial search. I am trying to implement this query in command prompt but it displays nothing

db.places.find( { loc: { $geoWithin : { $center : [ [x, y], 10 ] } } } )

Inplace of x and y i wrote longitude and latitude. I want to do spatial search around a particular longitude and latitude. What should i write in loc, x, y?

Please help!!!!

Thanks in advance.