Symmetric encryption uses same key for encryption and decryption, while assymetric encryption uses a public key for encryption and a private key for decryption.
Steps for encryption: get plaintext and public key, combine text with key to make ciphertext. Decryption: put ciphertext into private key to get the original text.
If you share your secret key, your encrypted data can be decrypted, meaning they can see whatever message you sent, which is pretty bad for you.