Before 2011, May the Fourth was just a regular day, passed by like any other non-holiday. However, in 2011, George Lucas decided to make amends for the Prequel Trilogy, announcing that they were non-canon, and that the Original, unaltered trilogy would come to Blu-Ray and Digital Services across the World!
Just kidding. Star Wars Day has, since its inception, been both a cultural phenomenon and marketing ploy for Disney, giving them an opportune time (every year) to announce information for any upcoming Star Wars projects. But don't let that corporate agenda disparage you; if you love Star Wars, celebrate.
Wear that Star Wars T-shirt or hoodie. Watch the originals on VHS (or burn the Prequels/Special Edition in a fire with your friends). Put on that stormtrooper armor you've been making for the last year and a half. Chances are, you'll find plenty of people doing a lot of the same.