How to join query in mongodb?

I have user document collection like this:

User {
   id:"001"
   name:"John",
   age:30,
   friends:["userId1","userId2","userId3"....]
}

A user has many friends, I have the following query in SQL:

select * from user where in (select friends from user where id=?) order by age

I would like to have something similar in MongoDB.