If you are a beginner, I suggest choosing a binance exchange, why is that? because I think binance is currently one of the exchanges with a very high exchange volume so you can feel more comfortable in trading with a lot of trading volume.
I agree with this, in binance, he can avoid kyc services which almost big exchanges require their traders to fills. He can start to any amount to trade but remember that he should not withdraw more than 2 btc if he doesn't want to fills kyc. Besides that, in binance, he can choose so many coins but of course, he needs to have skills to start trading.