You can block attacks with a shield or equipped weapon by holding M2. You can only block with a one-handed weapon if the weapon is in your right hand and your left hand is empty. If you are weilding two weapons, you can't block at all.

A blocked blow or arrow will still do some damage, and use up some stamina. Enemy power attacks cannot be fully blocked, though their damage and staggeting effects will be reduced. Shields are more effective at blocking then weapons, and can also block arrow damage.

As your block skill increases, you can block attacks more effectively, and with less of a stamina cost, You can also select perks that allow you to reduce the damage of spells and dragon breath attacks.

While blocking, you can perform a bash attack. Continue to hold M2 and tap M1 to perform a Quick Bash that has a chance of staggering enemies. Hold M2 and holdd M1 to perform a stronger Power Bash that sends enemies flying. Both kinds of bashes require Stamina. If your stamina bar is too low, you cannot bash.

Block quick, lighter attacks. Bash power attacks, when an enemy;s defenses are down, then quickly counterattack with a flurry of light attacks or a power attack of your own.

The following races get a +5 bonus to their block starting skill: Imperial, Nord, Orc, Redguard.

Fighter type characters might want to look at the following perks to take full advantage of blocking: Shield Wall, which increases the effectiveness of your blocking.  Power Bash, which lets you perform a Power Bash. Deadly Bash which causes bashes to do much more damage. Taking the Disarming Bash perk will give you a chance to disarm when you perform a power bash. Shield charge lets you spring and knock down enemies with your shield. Quick Refelexes causes time to slow down if you are blocking while enemy is doing a power attack. Deflect arrows cause arrows that hit your shield not to inflict any damage. Elemental Protecction lets your shield reduce frost, fire, and shock damage. Block runner allows you to move faster when you have a shield raised.