First you have to know how to sign up an acount to some exchanger like binance, bittrex, poloniex, coinexchange, cryptopai and many more crypto currency exchanger.
Second you have to deposit in that acount and wait a few minates to credit your acount.
Third you have to find which coins do you want to invest make sure that this coins is in low price before you buy it.
You can now start trading, Good Luck and Happy Trading.