When ए is added to a consonant, you add the symbol े above the consonant.
When ऊ is added to a consonant, you add the symbol ू beneath the consonant.
When उ is added to a consonant, you add the symbol ु beneath the consonant.
When ई is added to a consonant, you add the symbol ी to the right-hand side of the consonant (after the consonant).
When इ is added to a consonant, you add the symbol ि to the left-hand side of the consonant (before the consonant).
When आ is added to a consonant, you add the symbol ा to the end of the consonant (for example, न na becomes ना naa when आ is added to it).
अ does not change the consonant, so if you see a consonant without a modifying symbol, it will have this vowel sound.
X Research source Vowels in Hindi have two forms: one form for when they are used by themselves, and one form for when the vowel is joined to a consonant in a word. Hindi has 11 vowels, some of which are indicated by the use of diacritic marks, or symbols added to the letters of an alphabet in order to show different pronunciations.