Hi Saiyuki,
You have put that the mission is a "Request" for the gold, not a delivery mission which is different.
In a request type mission, you have to go and buy the gold from another station then deliver it, usually back to the station that requested the gold within the time limit to obtain your reward.
There would not be an indication that you have the required amount in your cargo hold unless you happen to have some there already.
Has your ship got cargo racks installed and how much space is there left for the cargo?
For a delivery mission then the goods are indeed put into your hold for you to deliver to another location within the time limit.
I hope that helps, if not PM me and I'll help you.
There are plenty of videos to get you started in Elite on YouTube, I would advise watching some of them before trying missions again as that may help a lot.