What is the law regarding charging tax on internet purchases?

It sounds like your friend is planning to make sales of goods that are subject to sales tax. (In New York sales tax is applied to tangible personal property). If yes, then she must register for sales tax purposes and apply for a Certificate of Authority at least 20 days before she begins her business. Once your friend is registered for sales tax purposes, she is responsible for collecting and remitting any sales taxes to the Tax Department.  She will have to keep detailed records of every transaction and to file sales tax returns. Should your friend engage in business without obtaining a valid Certificate of Authority, she will become subject to penalty up to $10,000.   (I assume that your friend creates goods that are not specifically exempt from sales tax in New York State.  I am also assuming she is not going to sell her goods to wholesalers exclusively.) If you have more questions, please call the Law Office of Yelena Kalika at (646) 707-2226.