There are three main types of islam the Shia and the Sunni and the Wahabi although we say the Wahabia are non muslims because they kill the sunni and the shia.
The shias and the suunis are closely related but there are some sunnis that think that we shia are kafur (Non Muslims)because the ignorant sunnis think we think that Imam Ali should have been Prophet no we dont this is untrue we think Peophet Mohammed is the rightful Prophet but
These are the two main differences.
As for the Wahabis we beleive that it was there leader that killed imam hussain he was called Yazeed(may he inshallah burn in hell) and the sunni believe that to and because both sunni and the shia mourn they kill us for example that bomb that went of in kerbala this year was the doing of the Wahabis. They hide under the sunni name which then breings conflict between shia and sunni who try to live in peace with each other.