Here is a list of guides and tutorials which can help you navigate or explore Nico Nico Douga, as well as the Vocaloid/Utattemita community. Note that these guides aren’t perfect and they are always revised in order to be updated with the site changes, etc.

An intro to utattemita (usual approach)
An intro to utattemita (anime approach)

Registering for a Nico Nico Douga account
Getting a premium account
How to browse Nico Nico Douga
All about Nico Nico Douga communities
All about Nico Nico Douga namahousou/live streams
Useful Nico Nico Douga-related terms/words/expressions

Guide to Buying Vocaloid/Utattemita CDs and Other Merchandise
Ordering from shops with no international shipping (Animate, Toranoana, etc.)
List of NND Indies and Vocaloid International Digital Releases