First of all, you probably aren’t expecting the Overlord to appear, without reading about it beforehand. The room is large and ominous, but you have to cross most of it to reach the dragon glyphs. The glyphs themselves are very distracting, glowing and creating swirling winds. So it’s easy to get ambushed by the Overlord, which is a serious recipe for death.
Secondly, the Draugr Overlord can use the very Shout you just learned on you, even though you haven’t yet gained the ability to use the thing. He doesn’t lead his attack with it, which gives you a bit of opportunity, but when he does Shout, you get staggered pretty badly, and with a two-handed sword in his grip, a delay like that is quickly fatal.
Third, unless you’ve been doing some side exploring, crafting, and other such, you’re probably only level 2 or 3 and wearing armor kludged together from the bandits and draugr you killed to get here. This is the hardest punch here- without a lot of skill in your armor and weapons, and especially a few talents, the Draugr Overlord is overwhelmingly overpowered. Even cowering behind a shield will only slow him down so much, and it’s unlikely that you have many healing potions by this point if you are low-leveled.
There are essentially two main points to defeating the Draugr Overlord, a fight which is a helpful bit of training for later major fights. The first is that you need to always stay on your toes. Even though the world of Skyrim is pretty and a lot of cool effects happen when you do something significant, standing and staring at it -will- get you killed. You can even get distracted by the cool visual effect his Shout creates, which stacked with the forced stun you go through will give him plenty of time to cut you into kibble. The second is that extra leveling is not just encouraged but practically mandatory to a certain degree. Now, this doesn’t mean that you have to help everyone and their dog and harvest every last Snowberry bush in the whole of Skyrim. But when you see an item, grab it. Look for things- lockpicking can even get you levels, selling and buying with merchants will level you, experience comes from crafting potions with Alchemy, which then enhance your combat lifetime more directly as well- just make sure you do stuff. You don’t have to do everything, but whatever extra stuff you choose to do besides kill things and not die, make sure you do it whenever you get the chance. It will save your life.
Now, it’s not impossible to beat the Draugr Overlord at low level- but it’s hard, and there are a few things you can learn from this fight. For one thing, the moment a fight starts, you have to have already decided: are you going to try to stay away from the enemy and kill them before they reach you, or are you going to charge in and start killing them immediately? The Overlord takes several seconds to get out of h is coffin before you can actually hit him, and you need to use those- either charging up and standing over him with your weapon ready, or backing off so you have the space you need. For the other thing, when you drop into your inventory, time pauses. Using potions to heal, applying poisons to your weapons- these actions don’t actually take any time. If you get hit and stunned, or you’re recovering from a mighty swing yourself, or even if you have a moment to move your hand to the inventory key while the Overlord chases you, use it to make sure you’re staying in fighting trim the whole time. Both of these points will come in handy for later fights, whether or not they are part of a quest.