I’m really sued to burst firing/ spraying sometimes at their body but I want to learn how to headshot how can I do this, also what is the best crosshair to use for getting headshots?

My friend just started playing val today so I joined him to team him how to play. But he doesn't know what to do as this is one of his first fps. Some random Skye starts getting mad in chat and swearing at him because he doesn't know how to...