You can see the [bremsstrahlung](https://en.wikipedia.org/wiki/Bremsstrahlung) at the left of the graph; there are two peaks, labeled $K\alpha$ and $K\beta$, which are due to inner orbital electrons being ejected from the K-shell of the atoms by the x-ray source.  The ejected electrons are replaced electrons from other shells, and the [characteristic energy](https://en.wikipedia.org/wiki/Characteristic_X-ray) of the two peaks is due to the energetic photons released when electrons "fall" into the vacancies.

The other peaks, further to the right, at higher angles, are the [x-ray diffraction peaks.](https://en.wikipedia.org/wiki/X-ray_crystallography#X-ray_diffraction)