VAT is a consumption tax applied across the EU, and if you sell to EU consumers it almost certainly applies to you. Here's the shape of it.
Place of supply decides the rate
For most B2C sales, VAT is charged at the rate of the customer's country, not yours. That's why a store selling across the EU has to handle many different rates.
What OSS does
The One-Stop-Shop (OSS) lets you report and pay the VAT you collect across all EU countries through a single return, instead of registering in each one. It dramatically simplifies compliance for cross-border sellers.
Digital goods are special
Digital products (downloads, licenses) have specific place-of-supply rules, so they need their own handling.
Automate it
Getting rates right by product and country, and producing OSS-ready figures, is exactly the kind of thing a platform should do for you. This is not tax advice — confirm your obligations with a qualified adviser.