Transaction in foreign currency (Q Mac)

I've seen all the back and forth about the inability to track investments in foreign currencies. All I want to do is enter a transaction in my register and have it converted. I see in the "Window" menu there is a choice called "Currency" with "currency pair", "exchange rate," etc. How do I enter in a pair of currencies and an exchange rate so I can enter the few transactions from when I travel in one currency and have them converted to my home currency? Thanks