IF

IF Function 
returns one value if a condition you specify evaluates to TRUE, and another value if that condition evaluates to FALSE

=IF(logical_test, [value_if_true], [value_if_false])

Example of Single Range
=IF(AND(A1>0,A1<11),“Valid",“Invalid") 

Example of Exact Value

=IF(A1=1,“One", IF(A1=0,“Zero",”Invalid”)) 

Example of Ranges

=IF(AND(A1>0,A1<11),“One to Ten", IF(AND(A1>11,A1<21), “Eleven to Twenty",“Invalid"))

Sources:

http://moodle.pshs-brc.edu.ph/