itunes

in my laptop hp i have itunes programe and i want to make a back up my iphone to the itunes in my labtop .

but when i finish back up they said there is an issue i don't know waht's wrong . then i delete itunes from my device and when i installed again it can't install. really i don't know how to make back up and how to instull itunes again to my device . help me please