So tax interviews - what are they all about? How does this procedure work exactly and how mandatory is it?

The main reason I ask is that I was planning on selling stuff on the website and I'm relatively young, in the sense that I'm still a legal adult but not older than 30, and I have no clue about taxes (in fact, the topic kind of intimidates me at present because, from what I remember, I was discouraged from asking and basically got next to no concrete information). As far as I understand from the description on the tax interview page, what it seems to be telling me is basically "if you don't live in the USA, we will deduct a percentage from your sales", but that's where my confusion begins: do I understand that correctly? What does the interview require and what's it for in general? Do I have to take it even if the tax percentage will remain the same (I live in a country that doesn't have a tax treaty with the USA at present)? Will the website do the aforementioned tax deduction for me and/or do I need to do something locally in regards to taxes (e.g. go to the tax office in my area)? I'm not necessarily asking for legal advice as I doubt people will be able to give it to me, but if anything I'd just like to have this part of the website cleared up in a way that I understand in order to better orient myself and see what responsibilities there are that I must potentially take care of, and avoid continuing if it entails responsibilities that are too much for me at the moment. The last thing I want to do is blindly head in, mess something up, and then get myself into trouble because I couldn't handle what came my way or unwittingly didn't account for something important.

Thanks!