Hi@akhtar,
Before creating the cluster, you need to plan first how much Node Group you want in your EKS Cluster. All resources, instance type, etc you need to select. I have attached one example below for your reference. 
apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig
metadata: 
  name: nadimcluster1
  region: ap-south-1
nodeGroups:
  - name: ng1
    desiredCapacity: 2
    instanceType: t2.micro
    ssh: 
      publicKeyName: mykey1
  - name: ng2
    desiredCapacity: 1
    instanceType: t2.small
    ssh:
      publicKeyName: mykey
Copy this code in a yml file and run the below command.
$ eksctl create cluster -f yml_file