Gold points

Gold points are the coins which you can only get for buying software. They are basically the premium currency in comparison to Platinum points.

Gold can be exchanged mostly for relatively bigger discount rewards (only WiiU / 3DS). There used to appear some rewards for game-download codes, occasionally; nowadays it's at most a 3DS theme (if not available for platinum instead). On the Switch eshop, you can use gold points directly for any purchase with a discount of 1 cent per gold point.

You get gold points for any digital purchase at the ratio of 1 gold point per 20 cent (5 points per buck, 5%). For this to work with WiiU or 3DS eshop, you need to have set up an NNID which is linked to your Nintendo Account.

Physical switch games also come with a redeemable points code that may give 1 gold point per buck (1%). This code can be only redeemd in the first year of the game's release  (in some regions in the first two years), according to the release date denoted in the Switch eshop. 

Gold points will expire after a year, at the end of the twelfth month. The oldest points available will be used up first. You can view your soon to expire points on https://my.nintendo.com/point/expiration.

The old system of getting gold points
Before March of 2018, gold points would not be handed out at a fixed ratio, but via specific Missions. You would get a specific amount of gold points for making a purchase in the correlating price range; some low prices would not net any gold at all, although temporarily discounted software would get evaluated at its default price.