Combat is the most important part of Bloodborne, with intricate features that can be the difference of an area being easy or difficult. Mastering combat is going to be the deal breaker of whether or not you like this game.
Stamina is used for everything from attacking and rolling to dashing and backstepping, so you need to make sure that you use it appropriately in order to prevent death due to the inability to avoid an attack. Luckily, Stamina regenerated naturally if you are not doing anything that uses Stamina, so make sure that you give yourself time to recover in between enemies.
When near a target you can press R3 to lock-on, allowing you to backstep and side-step easily around them. If there are multiple targets you can switch target with the D-Pad or press R3 again to unlock.
While this can be great for aiming your attacks, there are a few cases in which you may wish to not lock on. When?! Well, the lock on for most enemies is their head, meaning that when fighting large enemies with weaknesses in their arms or legs you may want to not lock on to focus on their weaknesses.
Pressing R1 will preform a basic attack, which are weaker attacks that use less stamina than most attacks. These attacks can be chained together, allowing you to interrupt the attack of enemies rather easily, but they still have their drawbacks.
Pressing and holding R2, on the other hand, is a much slower charge attack that does significantly more damage. These attacks do not chain well with basic attacks, but they do have the ability to stagger enemies. In addition to the normal controls for all weapons two-handed weapons, triggered with L2, have special properties.
When enemies are staggered they become open to visceral attacks, triggered by pressing R1 when directly in front or behind an enemy. These attacks are extremely powerful and their damage calculation is completely independent of your weapon, allowing you to do significant damage no matter which weapon you are using. Additionally, visceral attacks make you invincible to attacks from other enemies and will knock any surrounding enemies backwards.