Usa este método chato:
public void onEnable(){
File f = new File(getDataFolder(), "mensagens.yml");
FileConfiguration fc = YamlConfiguration.loadConfiguration(f);
if(!f.exists()){
fc.set("String", "&6String");
fc.set("Int", 5);
fc.set("Double", "5.12353");
fc.set("Boolean", true);
try{
fc.save(f);
}catch(IOException e){
e.printStackTrace;
}
}
}
Para pegar:
File f = new File(getDataFolder(), "mensagens.yml");
FileConfiguration fc = YamlConfiguration.loadConfiguration(f);
p.sendMessage(fc.getString("String").replace("&", "§"));
p.sendMessage(fc.getInt("Int"));
p.sendMessage(fc.getDouble("Double"));
p.sendMessage(fc.getBoolean("Boolean"));
Acho que você entendeu.
Deve ter alguns erros, fiz todo pelo fórum =P