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: https://docs.woocommerce.com/document/setting-up-taxes-in-woocommerce/ ) 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 (printful.com 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