AWS Service-Linked Roles? is confusing to new AWS Users ?

When we create a IAM Role, we input Role Name and attach Permissions ?

But when we create a new Service Linked Role? along with Name and Permissions: we need “Role for Which AWS Service”?

Scenario 1:

If I want my EC2 instance to access (Put action) a S3 Bucket

Then we create a new Service Linked Role Name: (ServiceRoleToS3BucketPutActionOnlyForAWSEC2)

The only condition is that you can only assign this Role to EC2 instances.