You can use Step Functions with the Serverless Framework in two ways.
First, by using the Serverless Step Functions plugin, you can include Amazon State Language for Step Functions in your serverless.yml file and deploy it using the Serverless Framework.
Second, you can use the Serverless Framework to create the AWS Lambda-based services that Step Functions will orchestrate.
https://docs.aws.amazon.com/step-functions/latest/dg/connect-to-resource.html