I would agree with reflector. Various trading-related social media channels, forums, articles, videos are good enough for getting some tips. But nothing more. Before choosing the exchange, you must do your own research. Define your goals and find a place that will meet your needs. I could suggest trying CEX. It's a simple and practical exchange which is friendly to new users. Also, they allow buying crypto for fiat money (https://cex.io/btc-usd). As for the sum, I think 500 usd would be enough for the start.