Many people mistakenly believe that the Immaculate Conception refers to the conception of Jesus. However, it is a doctrine of the Roman Catholic Church in regards to Mary. Essentially, the Immaculate Conception is the belief that Mary was protected from "original sin" and was sinless. They still teach that Mary was born in the normal way, only immune from inherited sin.
The Roman Catholic Church argues that the Immaculate Conception is necessary because, without it, Jesus would have received his human nature from one who was herself stained with "original sin". From her time in the womb, Mary was sanctified because of her special role in bringing the Jesus as God incarnate into the world.
One problem with the doctrine of the Immaculate Conception is that it's not taught in the Bible. Even Catholics would have to admit that scripture doesn't directly teach it. The Bible nowhere describes Mary as anything but an ordinary human female whom answered God's call to be the mother of the Jesus. Mary was undoubtedly a godly woman and surely a wonderful mother. But the Bible gives us no reason to believe that Mary was sinless.
What scripture does tell us is that Jesus was miraculously conceived inside Mary, who was a virgin at the time. That is the doctrine of the Virgin Birth. The Episcopal Church teaches that belief in the Virgin Birth doesn't imply belief in the Roman Catholic doctrine of the Immaculate Conception.