Simplify the following text for a Grade 6 native English-speaking person.
Original: They debuted with their `` Nul Book Standard '' EP and then their `` 123 Nul EP '' on March 10 , 2003 , and later that year released their first single , `` First Day '' , on August 4 .
Simplified: They debuted with their `` Nul Book Standard '' EP and then their `` 123 Nul EP '' on March 10 , 2003 . Later that year they released their first single , `` First Day , '' on August 4 .