Difference between photonView.viewID and PhotonNetwork.player.ID

I have received the list of players through PhotonPlayer.playerList. Now I need to send the message to the certain player. How I am able to do it? I assumed that it is possible with such method: photonView.Find ( PhotonNetwork.playerList[ index ].ID ).

But then I have read that photonView.viewId doesn't correspond to PhotonNetwork.player.ID.

Explain me, please, purpose of photonView.viewId and PhotonNetwork.player.ID: in what their purposes, and in what a differences?

Whether there is between photonView.viewId and PhotonNetwork.player.ID a strong interrelation?

Best regards!