Depends how your data is stored but there are several options

shiftout DataPin, ClockPin,1,[myWord/16,myHalfbyte/4]

shiftout DataPin, ClockPin,1,[mysystem/8,myDevice/4,myFunction/8]

shiftout DataPin, ClockPin,1,[bit1/1,bit2/1,.....bit20/1]

This is an example of how I shift a load of data to drive 64 LEDs

shiftout DataPin, ClockPin,1,[$00,TwoDigits,FourDigits/16,TempZoneID,TempZoneSource,$00,$00]

Hope that helps