I know that WhatsApp uses some kind of encryption to encrypt messages, but is it asymmetric encryption?
If not what kind of encryption does it use?
To answer your question, it uses both. Sessions are established via asymmetric cryptography (Curve25519) with users' public keys. Once a session is establish, symmetric cryptography (AES-CBC-256) is used along with hash authentication (HMAC-SHA256) to encrypt/decrypt and authenticate messages.