Why is hydroxide (OH) not H? -- ionic bonding/covalent bonding? what are they? whats the difference?

OH is an oxygen covalently bonded to a H atom, here the O and H each provide an electron to form the covalent bond. covalent bonding is the sharing of pairs of electrons between atoms/molecules. ionic bonding is the electrostatic attraction between oppositely charged ions, i.e. H+ Cl-, they do not share a pair of electrons.