Religiously the Sunni and Shia are very different because of what they believe in. Abu Bakr was the first caliph after Muhammad. The influence that these two groups had on the decision of who would be the new caliph was very large.
The Shia and the Sunni are alike in many ways. One being that they both strongly believed in the way things should be. Even though politically they disagree, religiously they believe in the same. Both groups follow the five pillars of Islam and the holy book, the Qur'an.
Hanafi (founded by Abu Hanifa)
Maliki (founded by Malik ibn Anas)
Shafi'i (founded by Muhammad ibn Idris ash-Shafi`i)
Hanbali (founded by Ahmad bin Hanbal)
These are the four major Sunni law schools.
