Thanks so much for the 5 star review!
I think what you are asking is how to set it so when a player joins that they get their own head in their inventory.
This can be found here under (How do I create custom skulls (player heads?):
https://www.spigotmc.org/wiki/itemjoin-getting-started/
However, I will try to cover what I can here;
Custom Player Heads are super simple to setup. Set the ID to SKULL_ITEM, and set the data-value to 3. The data-value being 3 means it is a player head.
Finally just add the skull-owner identifier as shown below and put the name of the player you want to be displayed on the skull. In the example a placeholder %player% is shown. This means the player that gets the skull in their inventory will show their own skin! So everyone gets their own skull, with their own skin!
Here is an item that will give each player their own head when they join;
https://pastebin.com/6Lmjc8cf
If you still need help feel free to send me a direct message and I will help you out!