I know the celebration is different in different areas of the country so any insight would be appreciated
Indeed... firstly to mention that Spain is not a "country", in the traditional sense, but an amalgamation of different cultures arising from different medieval kingdoms often with little in common -not even language! It so happens that long time ago, one imposed its will via military conquest upon the others and has maintained its grip -with plenty of ups and downs- to this day. However, there are lots of animosities... and culture, customs and heritage celebrations are not "commonly shared" despite some attempts otherwise.
Thus, for example, Oct 12th is not celebrated neither in Catalonia nor in the Basque Country, it's "just" a bank holiday decreed by the Spanish government. Period. Their national days are, respectively, "La Diada" on Sep 11th and the "Aberri Eguna" in Easter (Sunday) although, due to political disputes, the latter is an unofficial celebration. In both cases, on those national days, heritage and cultural displays and other celebrations are held across those territories.
In Andalucia though, despite also having its national day on Dec 4th, the feeling of Spanishness is very strong, much like in Castille -the "imposing" one-, and they do celebrate Oct 12th. Cultural visits and exhibitions, patriotic demonstrations and military parades are held. The military-related activities (parades, open-day visits, navy tours, etc) are celebrated in different cities across different regions --except the above mentioned Catalonia and Basque Country, where these led to general protests and unrest several years ago when the Spanish government organized one in Barcelona in 1981, and have since not attempted to do so again.
In Seville, for example, last year there were concerts by the Air Force Music Band, an exhibition and a couple of military acts (izada de bandera and entrega de placa). Note, however, all of them are not necessarily held on Oct 12th, but "within that week". Oct 12th though it's a bank holiday as mentioned earlier, therefore shops and businesses are closed. Tourist stuff (ie Real Alcazar, etc) is open as lots of locals take this day also to do "internal tourism". Restaurants are open and public transportation functions normally (albeit with less frequency, much like any regular Sunday across the year). This is not to say there might be exceptions so better check the specific website of the place you intend to visit to ensure it's not closed on that day.
Yet even in those places where the Spanishness feeling exists, for a number of years, the festivity of Oct 12th as a "celebration" has been questioned by some. Note that the Spanish National Day as such exists only since 1982, before that, Oct 12th was held as the "Day of the Spanish Race" -a term totally inappropriate these days due to its colonialist implications- as per the celebration of the day of the "discovery" of America by Columbus in Oct 12th, 1492 and was meant to "celebrate the brotherhood of the Spanish speaking territories across the Atlantic". Despite the attempt to whitewash this festivity, now is called simply "Fiesta de la Hispanidad", there are a number of voices, even within those regions that feel the Spanishness above mentioned, against this celebration for the repercussions that the so-called "discovery of America" had (colonisation, slave trade, looting and pillage, forced Christianisation, etc), like for example this march in Madrid just last year.