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 delete 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 Delete Account button.
You will see a confirm alert box press the blue button
You have now deleted the account.