End-to-end encryption ensures that only the sender and receiver can access the message, making WhatsApp chats safe from hackers, government, and even WhatsApp itself.
WhatsApp uses the signal protocol, which is highly advanced and ensures that intercepted messages appear as gibberish.
Group chats are also encrypted, but the system is more complex.
WhatsApp can see who users message and when (metadata), but they can't access the content of the messages themselves.