Are betting exchanges legal in India?

Yes, betting exchanges with valid licenses are completely legal in India.

What are back and lay bets?

In Exchange betting, a "back bet" is a traditional bet in which you wager on something happening (e.g., Team A Winning). A "lay bet" is the opposite of a back bet, where you bet on something not happening (e.g., Team A losing).

What is commission, and how is it charged?

The commission is a fee charged by the exchange betting site operators, typically for your winnings; each platform charges a different fee; for example, the Betfair betting exchange app charges a 5% fee on your net winning on an exchange market. However, in most cases, it's usually deducted from your profit on a winning bet.