All objects emit electromagnetic radiation, whatever their temperature. A cool object emits radiation just as a hot object does, but the radiation it emits is mostly infrared. The radiation from an object is a continuous range of wavelengths, not just one wavelength. Radiation with a shorter wavelength has a higher frequency and carries more energy.
The temperature of an object sets two things about this radiation. First, the hotter the object, the greater the intensity of the radiation it emits, which means more energy is emitted every second. Second, as the temperature rises the wavelength distribution moves to shorter wavelengths, so the peak wavelength gets shorter and the peak frequency gets higher.
A warm human body emits mostly infrared. A hotter electric heater element glows red because it also emits some visible light. A very hot star looks blue-white because it emits more strongly at shorter wavelengths.
