Making the index.php to display posts from a single category.

Hi, as you may realise I am not yet very knowledgeble in using WordPress. My probobly very easy question (Althogh I was unable to find out by readin different materials such as the loop action) is: How do I make my main page display posts from just one category? (i.e. I dont want all categories to be displayed on the same page, (unless in search) I want users to see just the posts from the News category when they come to the site)