Making a button with an icon instead of text

Okay, so in the GUI, I know that you can make a button. But first off, the button is blocky and grey and that doesn't work. I just want an icon that I can press and it does things. Is this possible? Thanks. It's not that big of a problem, but I'd certainly rather have it than a giant blocky button that has to have text inside of it. Thanks for your answers!