Answer:
The stars in the field of blue stand for the states of the union.
A star was added to our flag when each state was added to the United States. Until 1912 there was no specified pattern or arrangement for the stars. When the 48-star flag was adopted in 1912 the exact size, shape, and proportions or our flag AND the stars were specified.
When Alaska was added to the US we had a 49 star flag, for one year (1959). After Hawaii joined the US we had our current 50 star flag (1960). The 50 star US flag is the longest flying flag in US history.