Need advice for working out

Hi, I'm a 36 year old guy and I need some advice on working out. I never have before, I live 5 minutes from a gym I want to join. I have no idea though what to do to work out. I want to lose weight and make muscle. I have no idea what machines to use or exercises to do. Also if anyone has any advice for maintaining a healthy diet, I'd appreciate it. Thanks in advance!