AWS KMS How to use Decrypt function Java

My question might sound too obvious but I am new to Amazon KMS. After reading a lot of docs on AWS I understood that if I am using CMK directly for encryption and decryption I can directly do it by creating encrypt and decrypt request. But what I am not clear is when I generate a data key and debug using that,the documentation says I need to pass encrypted data key to decrypt API and I will get plain text key which I can use to debug text on my "OWN". I don't understand this part. Can anyone please explain this and give a small example on decryption using data keys. Thanks in advance

My Sample code:

public String decrypt(String encryptedTextString) {
    ByteBuffer encryptedText = ByteBuffer.wrap(Base64.getDecoder().decode(encryptedTextString));
    DecryptRequest req=new DecryptRequest().withCiphertextBlob(encryptedText);
    ByteBuffer plainText = client.decrypt(req).getPlaintext();
    return new String(plainText.array());
}

public String encrypt(String plainTextString) {
    ByteBuffer plainText = ByteBuffer.wrap(Base64.getDecoder().decode(plainTextString));
    EncryptRequest req = new EncryptRequest().withKeyId(new String(plainTextKey.array()))
            .withPlaintext(plainText);
    ByteBuffer encryptedText =client.encrypt(req).getCiphertextBlob();
    return new String(encryptedText.array());
}

AWSKMSCryprography() {
    this.setCredential(new ClearCredential());
    this.genrateKey();
}

private void genrateKey() {
    GenerateDataKeyRequest request = new GenerateDataKeyRequest();
    request.setKeyId(keyID);
    request.setKeySpec("AES_128");
    GenerateDataKeyResult dataKeyResult = client.generateDataKey(request);
    plainTextKey = dataKeyResult.getPlaintext();
    encryptedKey = dataKeyResult.getCiphertextBlob();

}