There is some early documentation here: http://wiki.dfx.io/display/XAI/PlumeDB

To test out PlumeDB go to http://www.sapienceexplorer.com

All the current PlumeDB RPC calls are listed on the left hand side.

This is the general flow for creating a plume and then adding and retrieving a data record using sapienceexplorer.com:

• 1 - plmcreateplume. This will create a new Plume DB (currently you can only create private plumes). Once you have created the new plume note the plumeid.
• 2 - plmlistproposals. Enter the plumeid from the plume you just created and you will see a list of proposals. Click 'Accept Proposal' to accept. Proposals if I understand correctly proposals from others to host your data for a fee.
• 3 - plmaddrecord. Now you can add records to your plume. To add a record just fill in the record form including the plumeid from the newly created plume.
• 4 - plmgetlasthashes. Enter the plumeid of the plume you created above. This will list the hashes for the last records you added in order of the most recent to oldest. Note the hash.
• 5 - plmgetrecord. Enter the hash that you noted above from the hash list. This will retrieve the data that you entered in the 'plmaddrecord' step

At this point there is not yet any official documentation of PlumeDB functions.