“split post”

Hello,
I new with wordpress, and when I post something, I tried to use the “split post with more tag” tool, but first of all, appear a line with more, and delete the rest of the comment, and then when I press more in the post, appear exclty the same information and no the rest. Why? and why I can go back to the original post? I mean, when appear the “more line” disappear all the rest of the text and I can’t see it anymore.
There are an easy way to split post?
Thanks!!!