Sanskrit is an old Indo-Aryan language once spoken throughout India. Many poems, epics, and prayers are written in it. Although not widely spoken anymore, it gave rise to many of the modern languages of India and influenced several more languages that are not related to it; Sanskrit is also still used as a language of culture and religion in India.
In the past, Sanskrit was written in a variety of scripts by people from various places. Today, a modified version of the Devanagari script has been agreed upon as a standard.
a A i I u U e ai o au aM aH (or a:) ka kha ga gha Ga (nasal "ng") ca cha ja jha Ja (nasal "ny") ta tha da dha na Ta Tha Da Dha Na (retroflex) pa pha (not "fa") ba bha ma ya ra la va ha
Wikner's introduction to Sanskrit is a good start.
Sanskrit: An Easy Introduction to an Enchanting Language by Professor Ashok Aklujkar is also recommended.