Accounts 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 update a account is to go to the Accounts on the Dashboard:
This will be the same on mobile as well. You will need to click on an account.
Now you need to click on the Edit Account button.
You can now fill the Name, About, Current Balance & Account Type field in then click the Save button.
You have now updated an account to be used in expense or subscription.