You'll need to set up a My Nintendo account first. I'm not sure it's available worldwide, but you could try setting up an account for the US or UK. Miitomo is also not available worldwide. Not sure there's anything can be done about that. If you can use Miitomo there are points available daily for changing clothes, listening to 10 answers, getting 5 hearts, getting 5 comments, answering 3 questions.
One-off points can be gained by linking an NNID, a Twitter account, A Google + account and a Facebook account.
Weekly points can be gained by visiting Miiverse, visiting eshop, signing in to My Nintendo, clicking on coin in My Nintendo, visiting the Nintendo Store and answering the "Everybody answers" question in Miitomo. You have to have your NNID linked to your My Nintendo account for most of that.
How easy all this is will depend on your region.
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To spend gold points, go to My Nintendo Rewards and redeem them. That will give you a code to input on a 3DS or Wii U. You'll have to spend some money though as the codes are only discounts and don't cover the whole cost.