Photons are tiny packets of light, Kl and have energy in the form of electromagnetism. They don’t have mass, but momentum – a property usually attributed to an object’s mass. The momentum of a photon is dependent on its frequency. Think of a photon as a little packet of energy made of oscillating electric and magnetic fields. Like any wave it has a frequency which determines the type of radiation it makes up.
If it’s a low frequency it might be radio waves; a high frequency could be X-rays. Another effect that makes light appear to have mass is that it interacts with gravity. Einstein’s Theory of General Relativity explains how stars and black holes have so much gravity that space and time around them is warped. So light travels in a straight line, but its path has become curved due to bending of space-time.