If you sell digital services (such as downloadable documents, training courses etc) through your own website/shop to individuals in the EU (non-UK) you must register for VAT when the sales of these services exceeds £8,818. This is because the ‘place of supply’ is deemed to be outside the UK.
You can register for the EU’s VATMOSS (Vat Mini One Stop Shop) to make this process a little bit easier, or you can consider selling through a marketplace that will deal with the VAT on your behalf. (Etsy, FastSpring and others can do this for you – there is a good list here.)
We would recommend planning ahead and deciding how you’re going to set up before you launch your products – you don’t want to get on the wrong side of the HMRC VAT team!