How do I calculate international sales tax for ecommerce

Hi! How are you? I am Taynah, and I am opening an online store using WooCommerce, in Wordpress. Whiting the plug-in settings there are questions regarding Sales Tax. (The specific questions can be found here: ) My situation is that I am a Brazilian, looking to sell products internationally, mainly to english speaking countries. The products will be manufactured and shipped by a third party company in the USA, called Printful ( is their website). They will handle all the inventory and shipping, so it will not come to Brazil. My questions is how should I charge sales tax in my WooCommerce store in relation to Printful, and besides Printful if I decide to use other dropshiping methods in the future. Also, I am a little bit confused if I should charge taxes according to where I am located, where Printful is located, or where my customers are located. And how do I find this out. As you can see your help is much needed! I hope you can understand my question, and thank you so much for such a wonderful service! Best Regards, Taynah