In order to place new orders in Coinbase, you require first your APIs to access your private data, check the following article How Use Private REST API.
Once you have configured your API keys, you can start to place orders
Place a new Market Order, buy 0.002 contracts of BTC-USD
oCoinbase := TsgcWSAPI_Coinbase.Create(nil);
oCoinbase.Coinbase.ApiKey := 'your api key';
oCoinbase.Coinbase.ApiSecret := 'your api secret';
oCoinbase.Coinbase.ApiPassphrase := 'your passphrase';
ShowMessage(oCoinbase.REST_API.PlaceMarketOrder(coisBuy, 'BTC-USD', 0.002, 0));
Place a new Limit Order, buy 0.002 contracts of BTC-USD at price limit of 10000
oCoinbase := TsgcWSAPI_Coinbase.Create(nil);
oCoinbase.Coinbase.ApiKey := 'your api key';
oCoinbase.Coinbase.ApiSecret := 'your api secret';
oCoinbase.Coinbase.ApiPassphrase := 'your passphrase';
ShowMessage(oCoinbase.REST_API.PlaceLimitOrder(coisBuy, 'BTC-USD', 0.002, 0, 10000));