Regarding ABAP

I am very new to ABAP so can you tell me what the following means:

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First Question----

DATA: L_0MAT_PLANT_ATTR LIKE BIW_MARC_S.

DATA: ZPACKSTYLE(30) TYPE C VALUE '0000001800'.

DATA: ZSECTOR(30) TYPE C VALUE '0000001806'.

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Second Question----

CALL FUNCTION 'CONVERSION_EXIT_ATINN_INPUT'

EXPORTING

INPUT = 'PACKAGESTYLE'

IMPORTING

OUTPUT = ZPACKSTYLE .

Third Question----

LOOP AT I_T_DATA INTO L_0MAT_PLANT_ATTR.

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Will rewards points ...!

thanks