Light has no mass. But black holes are able to suck light into it. So does that make light a tangible substance?
Mass and energy are different faces of the same thing. It is probably better to think that *everything* is energy. (But sometimes the energy is so compressed we perceive it as mass.) Remember light has momentum and exerts a pressure when it strikes a surface. And when something emits a photon of energy E, the emitter's mass decreases by an amount E/c?.
light has a kinetic mass.
Light has momentum and can knock a physical object ( electron ) from its orbit. It contains energy which you can feel when subjected to a beam of light. Which makes it definitely a tangible real thing. But is it a substance? That is different. You cannot fit a lump of light into a bottle and claim I have a bottle full of compressed light. If you stop light it ceases to have any existence. Hence it cannot be matter and from that presumably you could never call it a substance. Note that whether or not black holes can interact with light is not relevant to the question.
In order to understand how light gets pulled into black holes, you have to understand a little bit about Einsteinian gravity. According to Einstein, gravity isn't a force in the same sense that electromagnetism is a force, but instead is the result of mass warping spacetime. Basically, a massive body - like a planet, star, or black hole - bends spacetime around it. As light passes near the massive body, the light follows a *locally* straight path through curved spacetime. This is important to understand; as far as the light is concerned, it hasn't changed its course. But to a distant observer, the light's path appears to bend, because spacetime itself bends. Due to its large mass concentrated into a small volume, a black hole warps spacetime so strongly that any light beam passing through its event horizon is forever curved into the black hole, never to escape. I hope that helps. Good luck! EDIT: Steve4Physics has provided another correct explanation of the same phenomenon. That's the beautiful (and sometimes perplexing) thing about physics; there are often numerous correct explanations for the same thing.
