#assuming we have already on mongo terminal

// this will resulting no row
> db.users.find({'email':'marjuqi@gmail.com'}).pretty()

// copying Greg's data and store it into temp variable 'marjuqi'
> marjuqi = db.users.findOne({'email':'greg@gmail.com'})

// generate new unique ID for 'marjuqi' data
> marjuqi._id = new ObjectId()

// update some specific personal info for 'marjuqi' data
> marjuqi.name = 'Marjuqi'
> marjuqi.email = 'marjuqi@gmail.com'

// insert it into document
> db.users.insert(marjuqi)

// if needed, update/set another field
> db.users.update({'name':'Marjuqi'}, {$set:{'gender':'male'}})

// this will resulting one row
> db.users.find({'email':'marjuqi@gmail.com'}).pretty()