hello iam confused a and the how to using?

a-e-u-i-o for an b-c-d-f-g-h-j-k-l-m-n-p-q-r-s-t-v-w-x-y-z for a

An and A are indefinite articles. Both these mean one or any one. They qualify a singular countable Noun. 'a' comes before a singular countable Noun which brings with a consonant sound. 'an ' comes before a word which has initial vowel sound. Ex : A book, a car, a man An egg, an umbrella, an India..