Devanagari is a script to write languages in India like Hindi, Sanskrit and Marathi. deva signifies 'heavenly' and nagari 'script of the city' in Sanskrit. An often uses transcription variant is Devnagri.
Devanagari is partly phonetic in the sense that a word written in it can only be pronounced in one way, but not all possible pronunciations can be written perfectly.
a 'a' as in about
aa 'a' as in art
i 'i' as in pit
ii 'ee' as in wheel
u 'u' as in put
uu 'oo' as in soot
e 'a' as in rate
o 'o' as in old
When no vowel is written, 'a' is assumed. To specifically denote the absence of a vowel, a halant is used.
k kh g gh ch chh j jh T Th D Dh N t th d dh n p ph b bh m y r l v/w sh shh s h L ksh gy/dny
The letters above are pronounced as in English, with the exceptions of:
d 'th' as in the
Among these, 'L' and 'N' are not used in Hindi. The entire set is used in Marathi.
There is no distinction of case, i.e. no uppercase and lowercase letters.
The ITRANS notation  is a lossless transliteration scheme of Devanagari into English. The letters used to represent Devanagari alphabets in this notation have approximately the same pronunciation in English. It is widely used on Usenet. In ITRANS, the word Devanagari is written as "devanaagarii".
Devanagari is also used to write Nepali.
(Note: "Devanagari" is the most common transliteration. Others are "Devnagri", "Devanagri", "Deonagri"(rare).)