Varṇās are letters of the Sanskrit alphabet.
There are a total of 46 basic letters.
There are two main types of letters in Sanskrit- the स्वराः (Svarāḥ) which are the 13 vowels and the व्यञ्जनानि (Vyañjanāni) which are the 33 consonants.
Words in Sanskrit are made by a mixture of vowels and consonants to create a letter.
Also, there are two varṇās which come after a vowel and cannot be pronounced by themselves. These are known as the आयोगवाहौ (Āyogavāhau).