Shields and some melee weapons have a block ability. However, simply holding block does not fully protect you from frontal attacks like in other games. To complete a successful block, you need to intercept their weapon or projectiles with your shield/weapon.
You also need to be careful to fully conceal your body parts, because even if you manage to block a hit, the weapon’s hitbox can extend past your shield and hit you on uncovered body parts. Therefore, distance management is equally as important as blocking in the right direction. With this in mind, larger shields will offer a higher degree of protection due their their bigger sizes.
Currently, the only weapon that can execute a parry is the Longsword. If you successfully block an attack with the Longsword, you can quickly follow up with a higher damaging 2-sting riposte animation by clicking the Right mouse button.
Blocking and parrying requires a great amount of practice to pull of consistently, as you need to develop the spatial awareness around your shield/weapon as well as know your opponents weapon’s move sets.