The American flag dates from June 14, 1777.
That flag had 13 alternating red and white stripes and 13 stars
on a blue field representing the 13 original states.
The Continental Congress assigned symbolic meanings to the colours:-

"White signifies Purity and Innocence;

Red, Hardiness and Valour;

and Blue, Vigilance, Perseverance, and Justice."

Surprisingly red does not symbolise blood as on other flags.
From 1795 to 1818 two additional stars and two additional stripes were added to the flag to represent Vermont and Kentucky. It was soon realised that, with more territories on the way to becoming states,
adding yet more stripes would be impractical.
In 1818 Congress reduced the number of stripes to 13 and established the policy of adding an additional star for every new state.
The design was not standardized until 1912, and many variations of the flag were common during the 19th century.
The current flag dates from 1960, when a 50th star was added for Hawaii, the 50th state.
One day there may be more stars for aspiring territories like Puerto Rico and the Virgin Islands.

Or:-
In the U.S. flag, white stands for purity and innocence. Red represents valor and hardiness, while blue signifies justice, perseverance, and vigilance. The stars represent the heavens and all the good that people strive for, while the stripes emulate the sun's rays
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