PL SQL Data Types Oracle PLSQL Tutorial

Add characters to a string
RPAD is from the right side.
LPAD is from the left side.

v_tx:= lpad(string,length,extra string);
v_tx:= ltrim(string [,character]);
v_tx:= trim(LEADING|TRAILING|BOTH character from string);

SQL>
SQL> declare
  2      v1_tx VARCHAR2(20):='Hello!';
  3      v2_tx VARCHAR2(20);
  4      v3_tx VARCHAR2(20);
  5  begin
  6      v2_tx:= rpad(lpad(v1_tx,10,'*'),15,'*');
  7      DBMS_OUTPUT.put_line(v2_tx);
  8  end;
  9  /
****Hello!*****
PL/SQL procedure successfully completed.
SQL>