On the order panel, you can choose to place a market, limit or stop order. A market order will execute immediately at the current market price. A limit order lets you set your own price, as well as set some advanced order execution options. Stop orders allow you to set a trigger price for a buy or sell.
Select 'market' above the buy/sell buttons to place a market order. Choose "Buy" or "Sell" and enter the size of your order. You can set the size in any supported currency. Selecting "Buy" for example, and entering 100 as the amount, then setting the units to US dollars will buy one hundred dollars worth of the digital currency you have selected at the market price.
Select 'limit' above the buy/sell buttons to place a limit order. Enter the order size, and your price, then select the button to place your order. When you place an order, it will be shown in several views - including 'Open orders', the 'Order book', and the 'Depth chart'. A basic limit order may be partially filled and is subject to price improvement - you may get an even better price than you asked for.
GDAX offers advanced limit order types.
When selecting a limit order, expand the "advanced section" to reveal the following Time in Force policies:
Time in force policies provide guarantees about the lifetime of an order. These types of orders provide advanced options you may be familiar with when trading traditional assets.
Select 'stop' above the buy/sell buttons to place a stop order. This order type allows customers to mitigate losses that may result from a price swing. By placing an order to buy or sell once the price reaches or falls to a certain level, you can ensure potential losses are minimized. To limit losses to 5% for instance, set a sell stop order for 5% below the price you purchased at.
You purchase 1 bitcoin for $500, with the intention to sell when the price goes up. The price begins to move downward, so you place a sell stop order at $490. The price ends up falling 10%, to $450, but because you set a stop at $490, your loss is limited to 2%.
You sell 1 bitcoin for $500, with the intention to buy back in when the price drops. The price begins to climb, so you place a buy stop order at $510. The price ends up climbing 10%, to $550, but because you set a stop at $510, you've bought back in losing only 2%.
Stop orders execute as market orders when the market price reaches or falls to the target you specify. Since these orders are subject to current market conditions, there may be a discrepancy (or "slippage") between the target price you set, and the actual price at which the order is filled.