Kubadm init (version:1.13.0-00)--> asking for swapoff

Hi All,
I just started to learn and set up the kubernets 3 nodes cluster…i just want to get clear below points with you all help.

  1. is it mandatory to do disable swap: before kubeadm init…and explain clearly if not…
    2)what is taint,what it is doing…until we untaint ,nodes are showing in not ready state…why?–>using calico network for CNI.
  2. getting connection refused error after restarting nodes, if we hit any kubernets related commands.