Double Your Money Using cryptocurrency

Simple: Just buy low Sell high!

Go get a Coinbase https://www.coinbase.com/join/54f9d135a8fa471cd2000026 or other exchange that sells you BTC, LTC, BCH or ETH. These are the main cryptocurrency you will need to buy the other cryptocurrency with. BTC, bitcoin being by far the most common one. It is like the money most exchanges use like paypal or banks use USD, the dollar as their main money.
Then peruse a site like https://coinmarketcap.com/gainers-losers/ that list the top gainers and losers over the last 24hrs.
The biggest gainers could be tomorrow's losers and snatch them up for very little money.

You may want even invest in steem or SBD. Two of the cryptocurrency of steemit.