You can define a function that takes parameters, provide values to those parameters when calling the function. Here is a good example of a function with a parameter:

SQL> CREATE OR REPLACE FUNCTION GET_DOUBLE(X NUMBER)

2 RETURN NUMBER AS

3 BEGIN

4 RETURN X * 2;

5 END;

6 /

Function created.

SQL> SELECT GET_DOUBLE(36) FROM DUAL;

GET_DOUBLE(36)

--------------

72