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.
Are these mobile apps for iOS and Android devices?
I only tried the binance in mobile and it's good. I forgot if I could also set the alarm whenever I hit the target. I wonder what exchange app can do this. It's way way better if you have that feature.