Seat covers come in two styles: universal and custom-fit. You can buy universal seat covers right off the shelf at an auto parts store or order them online. Custom-fit seat covers must be ordered to fit your exact year, make, model and seat style. They're far more expensive than universal-fit seat covers. But they fit like a glove, stay put when you slide in and out, and are more comfortable. Plus, custom-fit seat covers include breakaway stitching so the air bag can deploy properly if your vehicle has side bolster air bags.
To get around the air bag issue and keep costs down, universal seat covers simply eliminate the fabric that would normally cover the seat air bags. Then, to reduce slipping, the manufacturers coat the underside of the fabric with an anti-skid rubber. That makes them a bit more uncomfortable to sit on for long periods. And they will inevitably slip out of place and wrinkle because they're not an exact fit for your seats.
Some universal size covers were made with special sewing which helps to deploy the airbag. Check with seller if their seat cover comes with this option if air bag deploying is one of your concern.