Scripts

SetGameVar("LevR", 1);
print("We set LevR to be a Set Game Variable");

LevR = GetHeroLevel('Raelag');

You are setting the in-game variable "LevR" to 1, so you have no reason to complain – you are not changing it anywhere else.
And the next line, LevR = GetHeroLevel("Raelag"), simply assigns the hero's level (the first one) to a completely different variable.
It should be done like this:

function HeroLevelSave()
SetGameVar("LevR", GetGameVar("LevR")+1)--We increase the variable with the hero's level by 1
end

SetGameVar("LevR", 1)
Trigger(HERO_LEVELUP_TRIGGER, "Raelag")

In the Combat script, it's also a little different:

function Start()
Level_R = GetGameVar("LevR") + 0;
print("Level_R is set as a level identifier for Raelag in combat and depends on LevR through Set and Get Game Var");
  if GetHeroName(GetAttackerHero()) == 'Raelag' then
    print("if the player's hero is the attacker");
    local mana = GetUnitManaPoints(GetAttackerHero());
    SetUnitManaPoints(GetAttackerHero(), 200);
    repeat sleep(1) until GetUnitManaPoints(GetAttackerHero())==200;
    if Level_R < 20 then
      print("If the level is less than 20, then");
      for i, creature in GetDefenderCreatures() do
        startThread(UnitCastAimedSpell, GetAttackerHero(), 4, creature);
        print("cast Stone Skin");
      end;
      SetUnitManaPoints(GetAttackerHero(), mana);
      print("restore mana");
    else
       print("If the level is 20 or more, then");
       for i, creature in GetDefenderCreatures() do
         startThread(UnitCastAimedSpell, GetAttackerHero(), 5, creature);
         print("cast Magic Bolt");
       end;
       SetUnitManaPoints(GetAttackerHero(), mana);
       print("restore mana");
    end
  end
end;

You were missing some "end" statements; I've added the necessary number. Also, your script (if it's as shown above) will only work if *we* attack, not if *we* are attacked.
You were missing one "end".