In order to configure Multi-Currency in Magento 2 take the following steps: 

1. Go to Admin Panel > Stores > Configuration > General > Currency Setup.

Magento 2 currency setup,currency options

2. Configure Currency Options.

  • Set the Base Currency the prices in the 'Admin Panel' are set in.
  • In order to choose the currency which will be shown to the customer by default, set the Default Display Currency. To be able to display currency based on customer Geo location use Auto Currency Switcher Extension.
  • The Allowed Currencies enables you to choose currencies that will be available to a customer on a Storefront.

Magento 2 Currency Options, Base Currency,Default Display Currency,Allowed Currencies 

Once you have finished with the Currency Configurations press the Save Config button.

Magento 2 Currency Setup Configuration

Read more about Currency Rates Configurations.