Either run your own node (thus, the localhost reference in the docs) or call a public one...
$ curl -s http://iota.bitfinex.com \
  -X POST \
  -H 'Content-Type: application/json' \
  -H 'X-IOTA-API-Version: 1' \
  -d '{"command": "getBalances", "addresses": ["HBBYKAKTILIPVUKFOTSLHGENPTXYBNKXZFQFR9VQFWNBMTQNRVOUKPVPRNBSZVVILMAFBKOTBLGLWLOHQ"], "threshold": 100}' \
  | jq
{
  "balances": [
    "0"
  ],
  "references": [
    "BTJRZDCMYEEQBMGKIGZFDFHQWIWTX9UYUFEOLYIHVVWM9HYRZPOZCKRQFNYDLNGTT9KZHGUTGNSNZ9999"
  ],
  "milestoneIndex": 328554,
  "duration": 160
}