create [or replace]
function function name (parameters)
return ...
is
...
begin
...
end;
SQL> create or replace
2 function getArea (i_rad NUMBER)
3 return NUMBER
4 is
5 v_pi NUMBER:=3.14;
6 begin
7 return v_pi * (i_rad ** 2);
8 end;
9 /
Function created.
SQL>