The following is the basic Devanagari alphabet:
A letter in Devanagari has the default vowel of /a/. To indicate
the same consonant followed by another vowel, additional strokes are
added to the letter, like in the follwing example:
In addition, a few other "diacritics" are used at the end of words.
To denote the nasal [-am], a dot is placed above the letter,
much like the /am/ letter. Similary, to write [-ah], two dots are
written to the right of the letter, like the /ah/ letter.
When a consonant ends a word, it is necessary to indicated that
the last letter has no vowel. To do so, a diagonal line, called
virama, is drawn under the letter. Letters with the virama
are called halanta letters.
To indicate just the consonant clusters,
the letters are fused together in a variety of ways, a process called
samyoga (meaning "yoked together" in Sanskrit). Sometimes the
individual letters can still be discerned, while other times the
conjunction creates new shapes. The range of possibilites is quite
high, and I will only give brief examples to illustrate the concept.
Links & Sites of interest to Devanagari or Sanskrit: