Iñupiaq is one of the Eskimo-Aleut languages, a part of the geographically massive Inuit dialect chain extending eastward through Canada to Greenland. It’s spoken in northern Alaska by roughly 3000-4000 people, mostly adults over 40. Ethnologue classifies Inupiaq into two languages, North Alaskan Inupiatun and Northwest Alaska Inupiatun (aka ‘Seward Peninsula Iñupiaq’), but others, like the Alaska Native Language Center, call them two dialects of the same language (with two sub-dialects each, for a total of four main dialects). ‘Iñupiatun’ is just ‘Iñupiaq’ in the similaris case, meaning ‘like Iñupiaq’ or ‘in Iñupiaq’.
Iñupiaq is the only member of the Inuit branch of Eskimo-Aleut within Alaska’s borders. Its neighbors to the west and southwest are Siberian Yupik and Central Alaskan Yup’ik, and to the south, Koyukon Athabaskan and Gwich’in (Athabaskan). See here for a nice map. To the east, it joins Inuktitut in the Inuit dialect chain.
Separate Iñupiaq materials are a bit hard to come by, and even most linguistic works tend to treat Iñupiaq as it were synonymous with Inuktitut. Native speakers of Iñupiaq tell me, though, that they have varying degrees of mutual intelligibility with Inuktitut. Written materials cannot easily be shared, because unlike Inuktitut, Iñupiaq does not use a syllabary (see Inuktitut syllabary here). Also, the Iñupiaq orthography, unlike those for every other Roman-scripted Eskimo/Inuit language, represents the uvular fricative /ʁ/ with the graph ġ, not r.
Like other Eskimo-Aleut languages, Iñupiaq is an ergative-absolutive polysynthetic language with quite complex morphophonology. It has an impressive amount of assimilation, both progressive and regressive.
Online resources are few, but they include Alaskool’s online Iñupiaq-English dictionary, an audio phrasebook, and the traditional story Maniiḷaq. You’ll need to download their font to view these properly; unfortunately, Unicode hasn’t crept its way into Iñupiaq computing yet, at least as far as I know. Most print sources can be found at the Alaska Native Language Center’s bookstore.
 One important but confusing issue in Eskimo/Inuit linguistics: Inuit can either be used as a cover term for all Eskimos or as the name of the Inuit sub-branch of the Eskimo branch of Eskimo-Aleut. In Canada, it’s poor form to use the term Eskimo to refer to the peoples or their languages (or so I hear), but in Alaska, this is not true. The Yupik peoples (Central Alaskan Yup’ik, Siberian Yupik, etc.) do not have that word in their lexicons, and naturally they don’t appreciate being called by a name that doesn’t even exist in their languages. The general term Eskimo is still the acceptable one used in Alaska. So materials that are labeled ‘Inuit’ might be Iñupiaq, but then again, they might not be.