Countries that earn much of their income from exports see their currencies react to the price of those exports.
When the commodity rises, foreign buyers need more of the exporter's currency to pay for it, which tends to support that currency.
Canada is one of the world's largest oil exporters. When oil prices rise, the Canadian dollar often strengthens, which tends to push USD/CAD lower.
Australia exports large volumes of iron ore, coal and gold, much of it to China. The Australian dollar often tracks metal prices and Chinese demand.
That is why Chinese economic data can move AUD/USD.
Gold is priced in US dollars. When the dollar weakens, gold becomes cheaper for buyers using other currencies, which tends to lift demand and price.
The link is strong but not fixed. In a crisis, both can rise together as safe havens.
Before trading a commodity currency, check the commodity behind it.
