Serverless Custom Resources vs AWS Cloudformation Resource Block

Hello all. So, I’m pretty new to Serverless and AWS CloudFormation in general, and I hopefully have a quick conceptual question that I’m trying to clarify and reconcile.

As a bit of a context, my background is in data science and analysis and am currently wanting to pursue more opportunities in cloud computing, architecture, and integrating ML models or data engineering tasks into a Serverless systems for automation.

As I’m going through various tutorials, I went saw on a strictly CloudFormation tutorial how resources are called in a CloudFormation template; however, in recent tutorial that involves Lambda and Serverless the Yaml code completely omits that in lieu of a Custom section that references bucket(s) being created and linked to the Lambda function. The “class”/tutorial I’m didn’t really clarify anything about that or why it’s different, or really much of anything about Serverless itself despite using it for their examples.

So with that, How does using Serverless changes the CloudFormation template and deployes? It seems potentially quite a bit, but it’s currently a bit opaque to me. I’d ultimately like to use this service quite a bit and deploy Lambda functions linking to various S3 buckets for more automation, so just trying to wrap my mind around how Serverless changes the the template and deployment. Can anyone give a bit of clarification on this?

let’s say there is a minimal service which take aws-sdk as dependency. jpg to pdf