from an accounting point of view:

if the interests are periodicaly debited from your account by the bank  (monthly or annualy for instance)

Debit a P/l account (an expense account) and credit the bank account

if the interests are just added to the initial amount of the loan at the end of the period

then debit the same account as above and credit the loan account (balance sheet account) 

I would recommend setting up a separate interest journal, but you can also just use any existing journals that make sense to you.

When you receive your monthly / yearly interest statement from your bank, either add a new bank statement and reconcile as Julio said or just create a manual journal entry for the interest.

Creating a seperate account allows for easier reporting / analytics when looks for data about your interest earned :)

Hello David Lumm

I think You can use the bank statement, 

First, create bank statement and add bank statement line with the amount by  bank interest,
Second, use button reconcile

In the widget of reconcile you must select one account to entry bank interest and press button 'OK' that created the journal entry