Every NMR instrument contains several important parts. A powerful magnet is required to induce the separation between spin-up nuclei and spin-down nuclei. The magnet surrounds a vertical cavity in which the NMR sample is placed. A probe within the vertical cavity transmits the radio frequency required to spin-flip the nuclei. The probe also receives the quanta of energy associated with the relaxation of the nuclei to their original spin-state. This information is transmitted to the NMR console as an electrical signal called an FID (Free Induction Decay). The computer attached to the NMR console mathematically converts the FID to a spectrum using FT (Fourier Transform).
The sources below contain more information regarding NMR instruments and have nice schematics of the instrument itself.
Linde Gas – has schematics of both a CW (continuous wave) NMR and an FT (Fourier Transform) NMR.
Youtube videos:
Basics of NMR by Royal Chemical Society – nine minute video reviewing all the basics of 1H NMR including the instrumentation.