please give me the explanation of this program

DATA: BEGIN OF LINE,

COL1 TYPE I,

COL2 TYPE I,

END OF LINE.

DATA ITAB LIKE SORTED TABLE OF LINE WITH UNIQUE KEY COL1.

FIELD-SYMBOLS <FS> LIKE LINE OF ITAB.

DO 4 TIMES.

LINE-COL1 = SY-INDEX.

LINE-COL2 = SY-INDEX ** 2.

APPEND LINE TO ITAB.

ENDDO.

READ TABLE ITAB WITH TABLE KEY COL1 = 2 ASSIGNING <FS>.

<FS>-COL2 = 100.

READ TABLE ITAB WITH TABLE KEY COL1 = 3 ASSIGNING <FS>.

DELETE ITAB INDEX 3.

IF <FS> IS ASSIGNED.

WRITE '<FS> is assigned!'.

ENDIF.

LOOP AT ITAB ASSIGNING <FS>.

WRITE: / <FS>-COL1, <FS>-COL2.

ENDLOOP.