Multi-currency enablement and corporate currency
Key Takeaway
All conversion rates in a multi-currency org are measured against one corporate currency: the currency your headquarters reports revenue in. Turning on multiple currencies is permanent, so plan the change first.
Every Salesforce org starts with a single currency, which the Currency Locale on the Company Information page sets. An admin can turn on multiple currencies so that records and users can work in different currencies. After that, the admin keeps a list of active currencies, and each one is linked to the corporate currency by a conversion rate.
One currency by default
By default, a Salesforce org uses a single currency. The admin picks the "Currency Locale" on the Company Information page, and all currency values on records display in that currency.