Didn't knew I had to, but just for you: Nationally it's easy, identify the customer, issue invoice then send product, pretty much it (simplified obviously). Intra-EU; same thing but some additional VIES and VAT, mostly still easy. Non-EU business, now it's basically a full export, with all the requirements and declarations that comes with.

Edit: Somehow, the comment got deleted although I replied to it? It originally implied I wouldn't be able to explain why it's easier, so I wrote the above to explain.