SQL> create or replace function max_salary return varchar2
  2  is
  3    last_name emp.ename%type;
  4    salary    emp.sal%type;
  5  begin
  6    select ename, sal into last_name, salary
  7    from emp
  8    where sal = (select max(sal) from emp)
  9      and rownum = 1; -- in case several employess with max salary
 10    return last_name||': '||salary;
 11  end;
 12  /

Function created.

SQL> select max_salary from dual;
MAX_SALARY
-----------------------------------------------------------------------
KING: 5000

SQL> drop function max_salary;

Function dropped.

SQL> create or replace procedure max_salary (last_name out emp.ename%type, salary out emp.sal%type)
  2  is
  3  begin
  4    select ename, sal into last_name, salary
  5    from emp
  6    where sal = (select max(sal) from emp)
  7      and rownum = 1; -- in case several employess with max salary
  8  end;
  9  /

Procedure created.

SQL> var last_name varchar2(30)
SQL> var salary number
SQL> set autoprint on
SQL> exec max_salary (:last_name, :salary)

PL/SQL procedure successfully completed.

    SALARY
----------
      5000

LAST_NAME
--------------------------------
KING