[H] Domain naming?

[DHSinclair]

Are there any entry level links that explain do's and don't's when trying 
to create/formulate a proper id/value/name for a private domain?

From the last several months I get the idea that a domain name is 
something like:

word1-dot-word2-dot-word3

IIRC, the "word3", in a commercial space, could be something like .com, 
.gov, .net, as I've seen so far. (do have the RFC and/or IANA docs that 
show listings). Wondering.
Best,
Duncan