Black image fade over image

I have an image on my home page (or index.html) and I want to be able to hover over the image then a black image fades on with a low opacity.

Example: http://ift.tt/1GGEszA - if you go to hover over one of the images (or products), you can see the fade sort of thing I am trying to acomplish. I am fairly new at HTML and CSS, along with scripts and stuff like that. I'm assuming it's something to do with CSS, eg, hover, etc.

Thanks in advance