Traditional arrangement of the Sanskrit alphabet
The main alphabet used by Sanskrit is the Devanāgarī, which can be divided into several parts according to diverse approaches. So, let us see the alphabet and learn how to pronounce the letters in the following section. One more thing, the "ḹ" is not considered here, because it is a theoretical and rarely used vowel. By 'theoretical' I mean that it was invented to maintain the pairs short/long: a/ā, i/ī, etc, so that the "ḷ" is not without its long counterpart.
One of the remarkable things about Sanskrit is that the consonants are syllabic, that is to say, they carry the vowel 'a'. Without the 'a' they could not be pronounced, because the 'a' is the supreme letter. Most of the vowels (except the Anusvāra 'ṁ' and the Visarga 'ḥ') can be pronounced by themselves, without the necessity of consonants or other vowels, but the consonants cannot be pronounced without vowels. This clearly speaks of an entire philosophical model hidden in these simple characters. The vowels and their sounds have predominantly to do with what is superior and independent, while the consonants (mainly those of the first and second groups) have predominantly to do with lower stages of the Creation. The topic is far more extensive, no doubt. This has only been a mere "hint" of a peculiar characteristic of the Sanskrit: it is a language extremely elaborated in total agreement with a science that hides itself behind it. This is the wonderful thing regarding this language. Lastly, the vowel 'ṁ' (denominated Anusvāra), just as its name points out, always comes after a vowel that gives it support (in the formal alphabet it is used, of course, the 'a' to give it support). The vowel 'ḥ' (denominated Visarga) also needs the vowel support, being represented in the alphabet united with the 'a'.
One more thing, apart from these characters that compose the formal Alphabet, there is a series of signs 'hybrid', which are the combination of two or more formal characters. For example:
त्त (tta) द्य (dya) ङ्ग (ṅga), etc. Go to Conjuncts for more information.