Wordpress/PHP Help - Grid/Catalogue/Sitemap

[divine]

What I basically want to achieve is a page that shows all the posts on the site, in a grid preferably, with just a title and maybe a picture.

So far, this seems like the best sounding solution but I can't for the life of me make it work, probably because I don't understand PHP in the slightest.

I get as far as;

Step 4) Use the code below on the template of your category page (in yourdomain.com/wp-content/themes/yourtheme/category.php).

before I get stuck. Mainly because I don't have a category.php page. Nor does any other theme I recall using.

So, thinking logically I made a page called category.php and pasted that code into it but that doesn't really work. It just shows a grid on it's own, away from the actual site. So i'm guessing I either need other code in that category.php page or I need to put that code elsewhere...

Anyone reckon they might be able to help or know of an easier way to achieve what I want?