Issuing an invoice- Freelance photographer

I do freelance photography irregularly on weekends and its usually small cash jobs worth 200-300 bucks. I have another potential job and the client wants me to issue an invoice to them.

I understand I can issue a personal invoice (like on my name since my business is not registered) . How do I handle the gst part of it? Do I not collect gst? If I do, how do I pay?