Problem

You would like to output some additional information (ie port number) in addition to the variable provided by Terraform.

Solution

Use interpolation of the Terraform variable using ${var} together with the rest of the string you would like to output, like:

output "kibana_endpoint" {
  value       = "http://${aws_instance.elasticsearch.public_ip}:5601"
  description = "The Kibana endpoint"
}

More information about the language https://learn.hashicorp.com/tutorials/terraform/outputs?in=terraform/configuration-language