I'm not a religious expert. It's an historical difference, starting practically with the line of descendants of the Caliphate, with Ali being the one who was supposed to take over or follow the Prophet in heading the Muslim community. This was the initial conflict or break. That's a very historical question. The main difference, in practical terms, is prayer. There's a slightly different manner of prayer, and there are adherents to certain rules and regulations, and specifically jurisprudence.
To me, as a secular person, no I don't see a difference. There are four different sets of jurisprudence within Islam, and I don't really understand why there's such strife. It's more of a political power play than it is a religious question.