What is the importance of Megasthenes in the Greek short book “Indika”?

This is a very poorly phrased question, Anon; hard to tell what you’re after.

Wikipedia: Megasthenes

Megasthenes (/mᵻˈɡæsθᵻniːz/ mi-gas-thi-neez; Ancient Greek: Μεγασθένης, c. 350 – c. 290 BC) was a Greek ethnographer and explorer in the Hellenistic period, author of the work Indika. He was born in Asia Minor (modern-day Turkey) and became an ambassador of Seleucus I Nicator of the Seleucid dynasty possibly to Chandragupta Maurya in Pataliputra, India. However the exact date of his embassy is uncertain. Scholars place it before 298 BCE, the date of Chandragupta’s death.

Megasthenes’ Indica survives only in quotations from later authors, such as Strabo, Diodorus Siculus, Pliny, and Arrian in his own Indica. The Wikipedia article links to

• Ancient India As Described By Megasthenes And Arrian by Mccrindle, J. W : an 1877 publication of the fragments;
• http://www.sdstate.edu/projectso… : PDF of the same
• http://www.shsu.edu/~his_ncp/Ind… : excerpt of Arrian’s Indica, citing Megasthenes.

Megasthenes and Ctesias are the first two Western sources on India, and Ctesias’ was Persian hearsay, so Megasthenes’ is the first account at first hand. It still had a lot of fairy tales such as “people with backwards feet, ears large enough to sleep in, no mouths, or other strange features”.

You’ll need someone with more expertise in history than my glance at a Wikipedia page, Anon, to work out how important Megasthenes’ account is historically. If that indeed is what you are after…