Not sure how skyrim series works

the question concerns the game "the elder scrolls v" ,skyrim,
i understand that the game is released for pc,
and now I see some "DLC" for the game,
like :
dawnguard, Hearthfire, and dragonborn.

may I ask...
are these "DLc" independent from the game skyrim?
or do I install them one by one to the original game for extended features?

forexample,
do I have skyrim+dawnguard+Hearthfire+dragonborn
as the most updated game in future?


thank you for answering