How to use the dumped data by mongodump?

You need to use mongorestore, not mongoimport … which is used for things like importing json, or csv, etc.

From the back-up-with-mongodump docs:

mongodump reads data from a MongoDB database and creates high fidelity BSON files which the mongorestore tool can use to populate a MongoDB database.

mongodump and mongorestore are simple and efficient tools for backing
up and restoring small MongoDB deployments, but are not ideal for
capturing backups of larger systems.

You can read more about mongorestore in the docs below; I’d take a look and read up on them as they are very helpful.

http://www.mongodb.org/display/DOCS/Import+Export+Tools#ImportExportTools-mongorestore

You can also check out http://learnmongo.com for tips and help!