Automagically.

If you sell to a Customer in their currency (different from yours) then you must convert the amount they owe you.  Unless they pay the same day (and sometimes even if they do) you will either gain or lose money due to the different exchange rate between the date of the Invoice and the date of the Payment.

Take the case of an American Company, dealing only in $USD, that sells to a European Company, dealing only in Euros.  AmCo converts $USD 100 to € 89.68 on January 15^th.  EuCo pays € 89.68 back to AmCo on February 15^th, but by this time the exchange rate has changed, and the conversion back into $USD is now $97.13.  AmCo has lost $USD 2.87.

This is how the Invoice is recorded:

This is how the Payment is recorded:

When the Payment is matched to the Invoice, this is the additional Journal Entry automatically created:

So Odoo manages this automagically for you – as long as you record exchange rates accurately (we actually recommend you synch with a web service but you are free to record your own rates).

See also https://www.odoo.com/documentation/user/13.0/accounting/others/multicurrencies.html