How did Charles Darwin spread the idea of evolution?

He didn't.

Charles Darwin did not like the rough and tumble of public debate about his idea, though scientific debate was another thing altogether. The debate had spilled over into the public arena and needed on the spot debaters, which Charles Darwin was not. So, Darwin's friends that he first convinced of the rightness of his theory went to bat for him. Thomas Huxley, Darwin's bulldog, was foremost among them, but there were also others. Hooker, Lyell, and Wallace were the other main defenders of the theory in Darwin's stead.