Nepali uses a script called Devanagari (/ˌdeɪv(ə)ˈnɑːɡ(ə)riː/) for writing. Devanagari is an alphasyllabary script and this script is used for writing Hindi, Marathi etc. Devanagari is written left to right horizontally, like English. It has 33 consonants and 12 vowels (other sources may count more or less depending on the method used).
Lessons on the Nepali script can be found here sorted according to your proficiency level. It is recommended that all of the parts are covered before advancing to other degrees of proficiency.