It hides you activity from any entity (ISP, governement, hackers ...)
If you're connected to ProtonVPN these entities won't be able to block or censure you; they won't be aware of what you're doing but according to the amount of data you're consuming they can guess: they can know if you're downloading things (but they won't be able to determine what), watching movies (but they won't be informed of which movies), or browsing classic websites.