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!

I am using mongodump, mongorestore for daily backups and restoring from backup. I have two .bat files:
First, for backup, where you need just specify host database name and backup folder:

SET host=localhost:27020
SET dbNameToDump=MyDB
SET backupsFolder=Backups

mongodump.exe --host %host% --db %dbNameToDump%

SET date="%date:~10,4%-%date:~4,2%-%date:~7,2%.%time:~0,2%-%time:~3,2%"
cd %backupsFolder%
md %date%

xcopy /e ..\dump %date%

rmdir /s /q ..\dump

Above bat file create folder with name like this 2011-03-31.11-17(yyyy-MM-dd.hh-ss) in folder Backups with dumped collections from specified database. In files explorer it looks like so:

Second bat file i use for retore specified dumped files(here you also need specify database name and folder with dumped files):

SET host=localhost:27020
SET dbNameToRestore=MyDB
SET restoreFolder=Restore

mongorestore.exe --host %host% --db %dbNameToRestore% %restoreFolder%

In files explorer:

In additional, i am using windows schedule to automate backup process.

Hope above information will be useful for someone.