The distance between two adjacent peaks on a wave is its wavelength. A photon travels as an EM wave having two components, oscillating as sine waves mutually at right angles, one consisting of the varying electric field, the other the varying magnetic field. A photon is said to be quantized, in that any given one possesses a certain quantity of energy. Some other photon can have a different energy value. Photons as quanta thus show a wide range of discrete energies.
Photons traveling at higher frequencies are therefore more energetic.
Consult a physics text for more information. The flux concept is related to power , defined as the time rate of doing work or expending energy. The flux density is proportional to the squares of the amplitudes of the component waves. Radiance is closely related to the concept of brightness as associated with luminous bodies. Thus, the Sun, a source, irradiates the Earth's atmosphere and surface.