Unlike other open-world adventure games where you can hack your way to victory, Dark Souls requires a lot more finesse. Essentially, you have to pay attention to how enemies influence you, and then react when you offer certain tells. At certain moments of their attacks, these enemies are vulnerable, and then you should strike. The same overall strategy applies to bosses. Do not panic, and you're fine.
To give you the best chance of winning, you'll want to make one-on-one combat scenarios as often as possible. Getting into battles with more than one opponent at the same time is a great way to get overwhelmed quickly. The best way to ensure these scenarios is to use the target system of the game to fight an opponent and then lure them into an isolated area.
One of the most important things to watch in combat is your endurance knife. Each time you attack, block, roll, run, retreat, or take damage, your stamina is reduced. As it fills up, it limits the number of attacks you can use in quick succession, which means you can not stand there constantly with your shield. Instead, you have to make your decisions in time and make thrifty decisions with your moves to give you the best path to victory.
The game offers different types of attacks that use different types of stamina. You also need to see if an attack makes you vulnerable to a counterattack and if this step is worth the risk. The worst thing you can do is rely too much on your sword or shield and lose stamina in the middle of battle. This will make you vulnerable, and things can change quickly.
In the end, however, it's okay to run for your life if you're in a situation that's too hard. If you have trouble staying alive, you may not be strong enough to pass this part of the game. Pull back, heal, fill in stamina and regroup. It's better to be safe than to be dead.