Well, the general “difference” between Sunni and Shias consists of authority: the Sunni think that God has left no authoritative successor, so the community must convene to determine what is acceptable in terms of interpreting the Qur’an and applying the law (on the grounds that the Prophet Muhammad once said that his community could not “go astray.”). The Shia accept that an infallible guide still exists in the figure of the Imam.
But “Sunni” and “Shia” are very broad, general categories. Islam, like every other religion, is locally rooted. So a Muslim in Morocco is quite different than one in Thailand. But even more than that, a number of different schools of legal though exist that a Muslim might affiliate with: Hanbali, Hanafi, Shafi, etc. Within Shi’ism there are also Ismailies, Zaydis, etc.
But then you also have matters of interpretation that lead to differences, like those between Usulis, Sufis, Shakyhis, etc. Or matters of reasoning, which lead to the Mutuzalis (who mostly no longer exist, but had an impact on various Muslim communities/thinkers).
My point is, if you want to know what is specific to your coworkers Islam, you need to figure out what - if anything - he further identifies with, as well as the specific form of Fiqh, method of Tafsir, and style of worship that the Imam of his/her mosque subscribes to.
