How do i buy a bus ticket

I’ve been advised to post this question here instead. I’ll be visiting Newark pretty soon, I’m german and this is my first time going to the US, so I’m not too familiar with the bus system. Not sure if this is a dumb question, but where exactly do I buy the ticket? I’m a little nervous to be taking the bus on my own, so I want to make sure I’m mentally prepared when i get there.