I got really confused about the graph of the relationship between wavelength and intensity of black body radiation. What does the peak stand for? And what does the graph tell us?How can we analyze it?
"What does the peak stand for?":
If you consider infinitesimally small ranges of wavelength values, the energy density (intensity) will be maximal at the peak.
"And what does the graph tell us?":
Considering a place of uniform temperature, with radiation in equilibrium with the surroundings, such as in a uniform temperature box, the graph tells us how infinitesimally small slices of wavelength values contribute to the radiation energy density (energy per volume). The area under the curve is the total energy per unit volume.
"How can we analyze it?":
We can integrate a portion or all of the curve to determine the energy density in a certain wavelength range.