When working with Python you can simply write a code and execute it in Lambda console. You can also upload the zip file.
When working with Java you have to upload the jar or the zip file to lambda and then run it.
The first steps as a starter can be
1. open AWS Lambda console and download one of the blueprints. You can use the blueprint and manipulate accordingly. 2. You can then create a zip file for the same and use AWS CloudFormation commands to get the zip file and deploy the serverless application.
Hope this helps.