Comprehensive knowledge on Blocking

When you are trying to block and have the RMB held down, you are suggested to make an attempt on a shield bash by clicking the LMB. This drains stamina, but at least you still deal some pain to your attacker.
In the case you have succeed in blocking an attack, you get less damage. This does not mean you have negated all incoming damage. Blocking just can reduce the damage.
When attacker aims to attack your back, the kind of attacks can not be blocked. Blocking frontal and side attacks will reduce the damage you receive. Moreover, a good block will give the defender an opportunity to launch a special counter attack.