There is a variety of Melee Weapons in SOS. Melee Weapons in order of Damage: Skull, Knife, Axe, Stone Axe.
Hold [Right Click] to Block. You can Block even with no Melee Item, though you will take a small amount of damage and risk infection.
Hold [Left Click] to do a stronger melee attack. This attack will also always have a horizontal attack animation, making it easier to fight monsters with a team and not risk hitting people next to you.
Hold [Middle Mouse] and release to throw the item/weapon you are currently holding.Thrown attacks with a melee weapon do significantly more damage, especially head shots. However, the weapon will lose durability at a higher rate per throw than a melee swing.
Headshots with thrown melee are a very good way to clear Hupias (monsters).