It is difficult to start trading this time because the market is on the downside, but you can buy and hold for a while after the price can increase. And if you are fine with that, I think you can try with binance, bittrex, and poloniex because I think it's good for the beginner since, on that site, you will find a big list of coins that you can buy.
It is never to lose heart when you are with bitcoin. They always go up and down and repeat this scenario many many times. Dont be afraid of low price, rather best opportunity to buy bitcoin.