Infrared has two equal parts working together that make it possible to take a spectrum. First, infrared light can be absorbed by bonds and different bonds have different ranges of wavelengths to form distinct peaks. This allows for "distinct peaks" for each bond in a spectrum.
Second, without the instrument, it would be very hard to record an IR spectra manually (and accurately). The spectrometer is able to differentiate between different wavelengths of light quickly with high precision.