Hi!
Sunni Islam and Shia Islam
Following the death of Prophet Muhammad (P.B.U.H), a dispute broke out over who would succeed as the first caliph. The Islamic community was divided over who rightfully deserved to be the next caliph, where one side demanded for Ali to hold the position, while the other group with beliefs that resonated with the caliphate being elected into position vouched for Abu Bakr.
This resulted in a split with those supporting the appointment of Abu Bakr were known as Sunni Muslims, and the group of individuals who demanded Ali to hold the position being known as Shia Muslims.
Hope this helps!