In order to place new orders in Coinbase, you first need your API keys to access your private data. Check the following article: How to 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));