When I roar it can break a glass window
This refer to how he’s going to win/own this rap game: with his voice/lyrics, powerful enough to shatter glass.
The volume required to break a wine glass is more than 100 db, a level that is difficult but not impossible to reach with just the voice. Normal speech is around 50 db. To break a glass window, it would take way more than 100 db. .
To help improve the meaning of these lyrics, visit "War Is My Love" by Kendrick Lamar Lyrics and leave a comment on the lyrics box