This is based very closely on the tutorial located at https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/GettingStarted.PHP.html
This code does not use a locally installed copy of DynamoDB. It uses one, via normal key/secret authenication, in AWS. You can generate keys in your personal account for DynamoDB access or, you can update the code to use a locally installed copy of DynamoDB. You can follow the directions at the link above to do that.
If you do use a remote AWS Dynamo DB, put your keys in the credentials.json file located in the config directory.
I used a newer version of the SDK than the one the tutorial uses. The only difference is the way the DynamoDB client object is created.
Happy Experimenting!