I would recommend reading basics of trading first.
Exchange platforms I am using without a problem and can recommend are:

1.Binance.com
2.Bitfinex.com
3.Poloniex.com
3.Kucoin.com

If you want to buy Crypro with Fiat I suggest:
1.Cex.io
2.Kraken

For tracking prices, the best site is coinmarketcap.com
Good mobile apps for portfolio management: Delta and blockfolio.