Where to place logo image code

Would someone mind taking a quick peek here: vm-world.net

I have a logo I would like to insert in the top left hand corner where the text presently is. I have the logo called logo.jpg inside the /images folder for the respective theme. I am just not sure in what .css file i should be putting the code, where exactly and what exactly the code should say.

Your help would be greatly appreciated as I have been forced into learning this.

Thanks