shia believes in Allah, prophet and all fundamentals of Islam.
shia believe after death of prophet God selects the successive for prophet who is the leader of Muslim community and people can not select it.
shia believe the Caliph (Representative of God in earth after prophet) is appointed only by God and can not be selected by people because God said in Koran: “Indeed, I will make upon the earth a successive authority.” (Quran 2:30)
this means only God can select an Islamic leader.
in shia they are only fourteen infallible (12 Imams and prophet and his daughter Fatimah Zahra (sa))
and all of them are the same and have no mistake and have the knowledge of everything (this knowledge is from God and by permission of God and is not absolute knowledge. absolute knowledge is only for God and they still do not know many things. but they know anything human may need to know.) and they never die and they hear all sayings and even thinks of all humans after their death by permission of God and they are intermediates between God and human.
and shia Muslims always support them and forgive their lives for them.
shia Muslims do not consider selection of Abubakr as Caliph valid because God did not select him. they believe God ordered prophet to declare Ali is selected as successor of prophet (Quran 5:3) and prophet did this mission in Ghadir event that was in last Hajj of prophet in his life and prophet did a speech for 120,000 Muslims participating that Hajj with prophet. the famous shia book Al-Ghadir is a collection of evidences and proofs for Ghadir Hadith from 100,000 sunni references and read all of 10,000 sunny books. one sunni scholar said if we want to reply Al-Ghadir book (by Allameh Amini) we should first destroy all our books.