To set exchange rate for different currencies:

• Settings > Exchange Rates> Add Exchange rate(s)
• Select target currency > Enter rate and save exchange rate

To set base currency or default language or show multiple languages on frontend:

Go to Setting > Channels > Edit Channel

• Go to currencies and Locales section
• Select all locales which you want to show on frontend
• Set default language to show on website
• Choose all currencies you want to show in frontend(Ctrl + Select)
• Set default currency
• Save Channel