How to Handle Your Shield Like a Pro!
Explains how to use the Shield
How to Handle Your Shield Like a Pro! is a book found within the Mabe Village Library in Link's Awakening. Like most of other books found within the Library, this book gives Link tutorial information - in this case, how to properly use the Shield.
Link's Awakening (Game Boy) & Link's Awakening DX
"'If you hold the Button down, you can defend your- self from enemy attacks, and you can fillip some enemies, too... Besides the standard shield there is also a mirrored variety which can defend against beams!'"
The book mentions that Link can hold out his shield to block enemies, and that the shield can flip Spiked Beetles onto their back, revealing their belly as a weak spot.
The book also hints to the upgraded Mirror Shield that Link gets later in the quest.
Link's Awakening (Switch)
"If you hold [R], you can defend yourself from enemy attacks, and you can push enemies too...
Besides the standard shield, there is also a mirrored variety that can reflect beams!"
Rather than mentioning that some enemies can be "filliped", the 2019 version references that Sea Urchins can be pushed safely with the shield, an essential technique at the start of the game towards recovering Link's sword on Toronbo Shores.