who are shia'a imams ?

why shiaa have 12 imams ? and these imams belong to who ?this app contain the story for each imam and his life story and its talk about imam hussein , imam Ali and the whole imams also this app isSuitable for children & kids to let them know about the imamsDua e Ahad,Dua e Kumay, Dua e Nudba, Ziyarat Ashoora, Ziyarats,
Price USD 0
License Free
Version 3.0
Operating System Android
System Requirements Requires Android 4.0.3 and up