Post excerpt problem

Hi,

I’m making my own custom theme (my first ever!). Out of the many questions i have, the first i’d like to ask is that my home page is showing the FULL content of a particular post. I don’t want it that way. I want only 2-3 lines to appear on homepage and if user wants to read full thing he/she has to click on post title and visit that single page and read everything. But for now he/she can read everything in homepage so no one would visit any particular post’s page. How do i rectify it?