Answer: The IF clause.
Explanation: This is the IF clause; you can use it as:
IF (something = true) then "something happens"
else "other thing happens"
Some example of it can be, suppose that your program reads a number X that the user inputs, then you can do:
If ( X > 5) then
print: "the number X is bigger than five"
Else
print: "the number X is smaller than five"
Where, of course, the statements depend on the language used, but the "if" clause works almost the same in every language.