The 50 stars on the flag represent the 50 states of the United States of America
the 13 stripes represent the thirteen British colonies that declared independence from the Kingdom of Great Britain, and became the first states in the US.
White signifies purity and innocence, (stripes)
Red, hardiness & valour (stripes)
Blue, the color of the Chief (the square/ rectangle) signifies vigilance, perseverance & justice