Buying Ether
It's important to note that cryptocurrency experiences volatility and is financial instrument. Always have a plan before deciding which cryptocurrency to buy or sell.

Step 1

Download Coinbase

Step 2

From the homescreen, click the blue button with arrows at the bottom of the screen. Then, select “Buy” from the dropdown menu. This will open up a list of different crypto assets offered by Coinbase for buying and selling. (Alternatively, you can navigate to the “Prices” tab from the homescreen, click the crypto asset of your choice, and click “Trade.”)

Step 3

Click on the option for Ethereum (ETH) — be sure to note the current trading price listed on the right hand side.

Step 4

On the next screen, decide how much ETH you want to buy and enter in the amount. You can also denominate your purchase in ETH. After deciding on your desired amount, click the blue “Preview buy” button.

Step 5

On the “Order Preview” screen, review all of the information. You’ll see the amount of ETH you’re preparing to purchase as well as the price. Note that the trading price can go up or down before you’ve finalized your purchase. You’ll also see your preferred payment method, the fee that Coinbase takes for the transaction and finally, the total amount you will be charged.

Step 6

If all of this information looks good to you, click the blue “Buy now” button to purchase your ETH. You will be brought to a confirmation page and an additional confirmation will be sent to your email address.
Excerpt from Gary Vaynerchuk's guide to buying cryptocurrency.