^^^ Gold is a subscription-only channel. You need Sky, Virgin, BT or TalkTalk television services, or Now TV, to access it.
The most popular way to get Now TV is through a Now TV Box but you can also get it on your computer or with mobile devices:
http://www.nowtv.com/devices-v3
However you need a valid 'Entertainment Pass' (£7.99 per month, with no contract) to watch Gold (and 10 other channels, as well as all the 'box sets' which come as part of the deal).
Gold is owned by UKTV which, in turn, is co-owned by the BBC. Thus their 'pay' channels help to fund the BBC as a whole, enabling them to keep producing new content.