Once a turn, if you have at least 1 hp, you heal for half your character level rounded up. EX. 1 health for level two players and 20 health for level nineteen players.

You have an armor class of 10 plus your constitution modifier plus your proficiency bonus.

The shield guardian is magically bound to an amulet. As long as the guardian and its amulet are on the same plane of existence, the amulet's wearer can telepathically call the guardian to travel to it, and the guardian knows the distance and direction to the amulet. If the guardian is within 60 feet of the amulet's wearer, half of any damage the wearer takes (rounded up) is transferred to the guardian. 

You gain no bonus for wearing the amulet yourself and you can deem someone worthy of wearing it if you currently have no master. 

When a creature makes an attack against the wearer of the guardian's amulet, the guardian grants a +2 bonus to the wearer's AC if the guardian is within 5 feet of the wearer.

You CAN benefit from this if you have a shield equipped and must have a shield equipped in order to assist someone else or else you will take the damage. 

Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) bludgeoning damage.

You can use your fist to attack twice. 

Must have both hands free, but there is one exception. If you have a shield in one hand, then you can use your Action and Bonus Action to muti hit. You will hit once with your fist and once with your shield, and it will do the same damage as the fists. 

The shield guardian starts off with 12 health, and raises the hit die of the chosen class by one size. For example, a d6 becomes a d8, but a d12 is unaffected.