Little private comment before I'll start to explain how I've managed to get it done: That was tough.
So, I've started by creating REST API in AWS API Gateway, named it kolo, and created methods for Get and Post, and a Get method is in /kolo/{user_id} indentation
Then I've created dynamoDB named 'users' with key in form of user_id, after that I've created a role in AWS IAM to give access to DynamoDB table
After that I've created two AWS Lambda functions, one for each method, called PostLambda and GetLambda (both available for you to see in thos repository in according folders)
https://15ktwrw855.execute-api.eu-central-1.amazonaws.com/api/kolo/{user_id_here}
curl -H "Content-Type: application/json" -X POST -d "{\"name\" : \"Nikodem\", \"age\" : \"19\"}" https://15ktwrw855.execute-api.eu-central-1.amazonaws.com/api/kolo