How do I install java 8 to get forge 1.12.2 working

I am very new to mineos so please help

This is a method i used to put java 8 on and it seems to be a pretty common thing atm just read around on here because there is some good info around if you read the forum.

what you need to know to achieve this method:

-How to FTP files
-How to unpack/extract a .tar archive

I’m trying to run MineOS on TrueNAS Core but It won’t Work with Forge 1.12.2 please help