Straight out of Help:-
Returns one value if a condition you specify evaluates to TRUE and another value
if it evaluates to FALSE.
Use IF to conduct conditional tests on values and formulas.
Syntax
IF(logical_test,value_if_true,value_if_false)
Logical_test is any value or expression that can be evaluated to TRUE or
FALSE. For example, A10=100 is a logical expression; if the value in cell A10 is
equal to 100, the expression evaluates to TRUE. Otherwise, the expression
evaluates to FALSE. This argument can use any comparison calculation operator.
Value_if_true is the value that is returned if logical_test is TRUE. For
example, if this argument is the text string "Within budget" and the
logical_test argument evaluates to TRUE, then the IF function displays the text
"Within budget". If logical_test is TRUE and value_if_true is blank, this
argument returns 0 (zero). To display the word TRUE, use the logical value TRUE
for this argument. Value_if_true can be another formula.
Value_if_false is the value that is returned if logical_test is FALSE. For
example, if this argument is the text string "Over budget" and the logical_test
argument evaluates to FALSE, then the IF function displays the text "Over
budget". If logical_test is FALSE and value_if_false is omitted, (that is, after
value_if_true, there is no comma), then the logical value FALSE is returned. If
logical_test is FALSE and value_if_false is blank (that is, after value_if_true,
there is a comma followed by the closing parenthesis), then the value 0 (zero)
is returned. Value_if_false can be another formula.
Example:-
=IF(A1>B1,1,2) - says If A1 is greater than B1, then give me 1, else give me 2