Air vents are usually in the attics on the side walls. These air vents keep air circulating in the attic which can help cool the attic in the summer and provide a drying out mechanism in the winter. It is import these vents are not blocked by any debris and it can be important to ensure screens are intact with the air vents to prevent rodents and insects from entering the house.
Get inside your attic and inspect your different vents to make sure there is nothing blocking any airflow. You might also want to check to see if there is an appropriate wire mesh to prevent birds, rodents and other things from entering your vents.
You should also inspect your attic vents from the outside. Some might be gable vents on the side of the home, while others might be roof vents coming through the attic. Be careful when using ladders and walking on the roof to inspect these.
Here is a video on how to put screens on the attic vents.