So, in a few words: Essentially, a talent agent is hired by the actor to represent the actor. A casting director is the agent of a producer (or an ad agency, etc.). They are hired by the producer or the end-client, and their allegiance is to that side of the production chain.
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.