everything depends on how you observe it or may be how you want to observe it.
$c$ is a constant and not light, if you target the photons you do need to pass to Planck's formulation $\hbar\dots$.
But to your question: it depends how how you observe them!
Photons can be observed as superpositioned waves.
Photons can be also observed as particle.
Photons are the elementary superpositioned waves or particles of light - or better say they are themselves light!
Photons are indeed elementary superpositioned waves or particles that package energy.
The formula above says that photons would have also a mass equivalent. However it does not say how and under which condition you may convert photons in your lab to mass particles.
But what makes up a single photon? My favorite answer would be: the probability of meeting it at a location or with a certain energy.
Hope this helps.