They call casting people directly to get you work, and frequently casting people call them to fill work needs when they are very busy. For example, an extras casting director may have to book fifty extras quickly. Essentially, they book the shows for the extras casting director.
Can I wear jeans to an audition?
You don’t need to dress like you’re going in for a corporate interview here. Your clothes shouldn’t be a wrinkled mess, but you also shouldn’t be wearing business attire to an audition. A good pair of jeans can go a long way, and it’s worth investing in a pair for auditions alone.