methodin

// Adding a user auth to a DB (read/write, add true as a third param for read-only)
use somedb
db.addUser("username","pasword")

// Update an entry (don't forget $set or it will be replace only with what is provided)
db.gadgets.update({key:"Some criteria"},{$set:{weight:17.6}})

// Dump a database/collection
mongodump -d databasename -c collection -o .