SCART, an acronym for "Syndicat des Constructeurs d'Appareils Radiorécepteurs et Téléviseurs," is a European audio/video connection standard. Similar to VGA (Video Graphics Array) cables, SCART cables separate video signals in RGB (Red Green Blue) streams. Like a VGA cable, you'll need a modulator if you want to convert a SCART cable's digital signal into an analogue signal for transmission over a coaxial cable.
Connect one end of a SCART cable to the SCART port on your SCART-based audio/video device --- align the cable's pins with the port, and then push the cable into the port. Connect the opposite end of the SCART cable to the SCART port on your RF modulator.
Connect one end of a coaxial cable to the RF modulator's "Out" coaxial port. Connect the opposite end of the cable to the coaxial "In" port on your output audio/video device.
Plug the barrel connector end of the RF modulator's power supply into the power "Out" on the back of the RF modulator. Plug the transformer end of the power supply into a wall outlet.
Toggle the channel button on top of the RF modulator to either "3" or "4." Match the selected channel on your audio/video output device --- switch its channel selector to either "3" or "4." If your output device is a television, change the television's channel to match the channel set on the RF modulator.
Power on the RF modulator, SCART input device and your audio/video output device.