Soffit vents are the vents under the roof overhang. These vents allow cool air to be drawn into the attic. When the air heats up, it naturally flows out the roof vents. Pull the insulation back just a couple of inches from the soffit vents to make sure that they are not blocked. If you do not have soffit vents, you should add them.
Many houses have only gable vents in the sides.
These type of vents are not particularly effective for exhausting the hot air. The best type of roof ventilation is a combination of soffit vents and a ridge vent along the entire length of the roof. Ridge vent comes in rolls or long strips and it is easy to install. Do not block off the roof vents in the winter to conserve heat. The insulation on the floor of the attic should take care of blocking heat loss.