They typically pull air into the heat-sink from inside the case. Some coolers can then expel that hot air straight out the back of the video card outside your case. Some cards expel the hot air right back into your case.
Your card appears to pull air from inside your case, across the GPU heat-sinks and then expelled out of the case via the exhaust port of the video card. One of the better designs.
edit - biohazrdfear is correct.... ACX cooling means air is being pulled from inside your case across the heatsinks and then where it goes is probably... everywhere. Some out the back and some right back into your case. You will want good airflow in your case with that card.
That type of graphics card takes air from the inside of your case, and blows it towards the bottom of your case. This is what you call a "non-reference" card. EVGA took their own design and cooler, and applied it to the card. Then there are Reference design cards. These are the cards that are not modified by third party sellers, and have only one fan that sucks air in and pushes it out the back of the case. This leaves no air in the case.