Sub page “read more”

Hi all,

This might sound stupid, but how do i write a piece of text on the main page, and continue wriing on the “read more/comments page” So the users sees a couple of lines on the main page, and have to click read more/ comment to see the rest. I know that i can select a number of lines on for the frontpage, but there has to be a way that i can select what i want on the main page and what i want on the “read more” page.

Help please