Since you are new, I recommend visiting
CoinMarketCap, a site which shows many cryptocurrencies and its value, and you should monitor the prices and try predicting whether the price will increase or decrease.
To start trading, you can go to exchange sites like
Poloniex or
Bittrex, Polo is easy to use, Bittrex has more coins to choose from, your choice.
Start by trading with 1 or 2 coins, especially those with higher trading volume, which means the more popular ones, so that you do not buy coins that just drops in value as soon as you buy.
Start trading with a small amount. Soon, you will get some experience which then you can trade a bit more, with more coins. Best of luck!