Dump a single collection
mongodump -h "mongodb0.example.com:27017" -d dbname -u user -p password -c collectionname -o path-to-output
Make a backup (dump all collections)
mongodump -h "mongodb0.example.com:27017" -d dbname -u user -p password -o path-to-backup
Restore a backup
mongorestore -h "mongodb0.example.com:27017" -d dbname -u user -p password path-to-backup