Basically you have each carbon atom bonded to three other carbon atoms so you end up with electrons that are delocalised sort of hovering above and below the sheet of atoms. That means if you apply a voltage across it there is nothing really stopping the electrons from flowing - which is the definition of a good conductor. Graphane and graphene are different things - graphane is like graphene but has hydrogen's bonded to the sheet instead (localising the delocalised electrons to the covalent bonds between the hydrogens and the carbons.) Be careful saying that there is no electricity conduction because of covalent bonds - graphene also is bonded covalently, its all about the delocalised electrons.