So you save transaction fee, if you understand how the trading works on an exchange and how to place a limit order for buy or sell. Vamshi Vangapally. In most circumstances the Coinbase system can authenticate this automatically, meaning that the process only takes a few minutes! So now that you know how to buy coins on Coinbase, the next part of my guide is going to show you how to transfer from Coinbase to GDAX. After verifying your email address, you will be asked to provide a phone number.