https://www.spigotmc.org/resources/categories/skript.25/ Here is a link to the Skript section on Spigot Resources have fun.
A simple search of the word "Skript" will land you here(Skript home page): http://njol.ch/projects/skript/ For a download you can get it here(Download link of Devpage I found on home page): https://dev.bukkit.org/projects/skript I hope that is enough information.
You are getting that error because your that version of Skript does not support your server version. Also, we really only need the error, not the whole log
