=Sheet1!A1
=IF(Sheet1!A1="","",Sheet1!A1)
=IF(O8=Dropdown!AR84,Dropdown!AU84)
=IF(condition to check, what to return if condition true, what to return if condition false)
=IF(O8=Dropdown!AR84,Dropdown!AU84,"")
=IFERROR(VLOOKUP('Global Setup Form'!T8,'Global Dropdown'!A:B,2,FALSE),"")