findOne():Returns one document that satisfies the specified query criteria. If multiple documents satisfy the query, this method returns the first document according to the natural order which reflects the order of documents on the disk.
syntax:
$query=array('name_filed'=>$name_any); // in php
>db.collection.findOne($query); //mongodb terminal
But In case of find(),
Returns all document which matches criteria or query;
>db.collection_name.find($query);