Hydrogen can form one covalent bond. This is because a hydrogen atom has one electron in its outer shell and needs one more electron to achieve a stable configuration resembling that of the nearest noble gas, helium.
When hydrogen bonds with another atom, it shares its single electron with that atom, allowing both atoms to fill their outer electron shells to reach stability. This sharing of electrons is what we refer to as a covalent bond.
In conclusion, due to its single electron, a hydrogen atom is capable of forming exactly one covalent bond with another atom.