1) Create an account at Coinbase
2) Connect your Coinbase account with a bank or credit card and move some money to your Coinbase account
3) Purchase BTC/BCH/LTC/ETH at a comfortable price.
Feel free to stop at this point if the long term goal is to liquidate back to USD.
4) Explore/invest/gamble in "alt coins" at an exchange like Bittrex or Binance. Pick an exchange and create an account.
5) On the exchange, find the wallets page and get your BTC/BCH/LTC/ETH address. Copy this address to Coinbase and transfer your funds to the exchange.