Tutorial for creating new head mesh

[Vajurilla]

Hello I'am new and noob, but want to try to make mod. I'am sorry for my bad English. However, I need help and want someone to explain this for me.

I want to creat a new head mesh for my custom race ,but i don't understand how to do a facegen for new head.

I open in the game file, There are file name malehead.nif , malehead.tri, MaleHeadCustomizations.tri, maleheadraces.tri.

I don't known which is the head main file. Could someone explain about 4 file for me please.

 

and

 

Could anyone point me towards a tutorial for creating new head meshes and facegen?

 

Thank you.