AES encryption, what are public and private keys?

In AES encryption (.net framework), how are the public and private keys used?

Are the public and private keys combined to form a full key, and then the algorithm uses the public + private key to encrypt the data?

(simplified keys used below for example purposes)

e.g. public key = 12345 private key = 67890

so the key used when generating the encryption result is: 1234567890