Unrealized gain or loss accounts are used when the revalue currency function is called in the general ledger. For example - if you have a transaction created in a foreign currency  (CAD) and your Functional Currency is (USD)  then at month end if the rates have moved against you there would be an entry that would debit the unrealized gain or loss account for the module and credit the unrealized gain or loss foreign currency offset.

1. Log in as Admin user
2. On user’s menu panel, go to System Manager folder then click Company Configuration
3. Click the Multi Currency tab on System Manager module
4. Select the Unrealized gain or loss account for each module.
5. Unrealized gain or loss accounts must be accounts setup with the "Unrealized Gain or Loss" category in the general ledger.
   

Note:

How to Add a Currency Exchange Rate Type