Below is a simple Terraform script block to create a Security Group in AWS.

resource "aws_security_group" "Sample-App-Security-Group" {
  name          = "sampleappsg-123"
  description   = "Inbound and outbound traffic for sampleapp service"
  vpc_id        = aws_vpc.id

  ingress {
    from_port = 0
    protocol  = "-1"
    to_port   = 0
    cidr_blocks = ["10.0.0.0/8"]
    ipv6_cidr_blocks = ["::/8"]
  }
  egress {
    from_port = 0
    protocol  = "-1"
    to_port   = 0
    cidr_blocks = ["10.0.0.0/8"]
    ipv6_cidr_blocks = ["::/8"]
  }

  tags {
    Name = "Sample App Security Group"
  }
}

You can read up more about all the possible arguments in the AWS Security Group Terraform Reference.