Also, if you're unfamiliar with CSS generally, the 'conventional' approach (as opposed to img tags in markup, or characters in an icon font) would be to use a sprite. This is also advantageous from a frontend performance standpoint as you avoid additional network overhead in getting individual graphics down to the client.
Where you absolutely cannot avoid a graphic (like having an icon or something), the use of pictographic fonts is becoming increasingly popular. Mostly due to reasons of scalability to different resolutions on different devices.