Amazon Elastic Load Balancer is a part of IaaS.
You will have to manage your own instances and deployments to use it.
Amazon Elastic Beanstalk is a PaaS: you only provide it with your artifact and it manages deployments and scaling automatically.
Elastic Beanstalk uses ELB internally, but you don't have to manage it.
If your app could be supported by Elastic Beanstalk, you probably should use it instead of configuring and managing your own environment with ELB.