Quick explanation: think of wavelengths in terms of energy. Short wavelength = high energy, long wavelength = low energy. So in this case in the UV/optical (HST), you mostly see the high energy photons from young, hot stars. In the near-infrared (NIRCam), you mostly see slightly lower energy photons from older, cooler stars. In the mid-infrared (MIRI), you see the even lower energy photons from dust that absorbed higher energy photons from stars (blocking us from seeing them) and then cooled and radiated that energy away.