I would like to ask what is a Sales Tax Licence, sometimes called Sales Tax Permit and how can I make an use of it as a non-US resident willing to begin business in USA. Is it a requirement in order to sell services on internet or is it only for physical goods ? Thanks
Sales tax permits come from the state in which your business is operating. You need a business license first for them to issue you one.
US sales taxes are collected by the business and remitted to the government, you need the permit in order to do this.
A bigger question is whether it's legal for you to engage in business in the first place. What is your visa status?
Disclaimer: I am not a tax specialist
You probably need a sales tax permit if you're going to sell goods, since just about every state taxes goods, though some states have exemptions for various types of goods.
For services, it gets tricker. There is a database here that lists what services are taxed in what states; in Wyoming, for example, cellphone services and diaper services are taxed, while insurance services and barber services are not.
For selling over the internet, it gets even dicier. There's a guide on nolo.com that claims to be comprehensive; it states that the default rule of thumb is that if you have a physical presence in a state, such as a warehouse or a retail shop or an office, you must collect tax on sales in that state. Given your situation, you probably only need to collect sales tax on customers in Wyoming. Probably.
In any event, I'd advice having a chat with an accountant in Wyoming who can help walk you through what permits may or may not be needed.