I'm the confused in a, an, the

We will use these three articles in three different conditions. E.g. If there is a word which starts from consonant sound like bat,lamp, or boy. Then we'll use a, for example, This is a bat, This is a lamp, or This is a boy. And We'll use an for the word which starts from vowel sound then we'll use an, for example, an orange, an umbrella, and an apple. After that we'll use 'the' with a proper word, for example, The Pakistan, The India, and The Sub-Continent etc.