this statement is used to sort the internal table.

yep its correct its is used for sorting internal table.

synatx :

SORT <itab> by <field> Ascending/descending.

This statement sorts an internal table itab. As standard, 
numeric and byte-type components are sorted by their value 
and character-type components according to their binary 
representation code page). Textual sorting of character-
type components is performed using the addition AS TEXT. 

Syntax 
SORT itab [STABLE] 
          { { [ASCENDING|DESCENDING] 
              [AS TEXT] 
              [BY {comp1 [ASCENDING|DESCENDING] [AS TEXT]} 
                  {comp2 [ASCENDING|DESCENDING] [AS TEXT]} 
                  ... ] } 
          | { [BY (otab)] } }. 

Thank's and Regards,
Shreeshail Diggi
SAP Technical Consultant Infinite India