First, create the data bag. Name it whatever you want.

    knife data bag create BAG

Next, create data bag JSON files in subdirectories by data bag name. Then
upload the items to the Chef Server with knife:

    knife data bag from file BAG FILE

For example, create a bag named 'apps' with an item named 'instiki':

    mkdir data_bags/apps
    echo '{ "id": "instiki" }' > data_bags/apps/instiki.json

Then upload it to the server:

    knife data bag from file apps instiki.json

For more information about data bags, see the Chef wiki.

http://wiki.opscode.com/display/chef/Data+Bags