Merchants can be used on Expenses & Subscriptions. They help separate the data so you can see how much your expenses are for going out ETC...
The first step to create a merchant is to go to the Merchants on the Dashboard:
Now you will need to click on the merchant that you're wanting to edit.
Click on the Edit Merchant button under Actions Box.
You will fill the Name & About fields in then click the Save button.
You have now updated a merchant to be used in expense or subscription.