Rear and top should be exhausts, front and bottom should be intakes. As for the side, I'd say it depends on the type of Graphics card you have, you should just experiment a bit and see, fairly certain of the other 4 though.
My 560ti runs at 99% 24/7 and doesnt go above 80C, my fan is connected to the PSU with a 'quiet' connector for low speed.
Just go with the front and side as intakes. You would prefer the bottom to exhaust not bring in dust but a fan exhausting will just pull the air from the front fan. If you can use a filter then it could be an intake, but I doubt you will need it.