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 create a category is to go to the Accounts on the Dashboard:
This will be the same on mobile as well. You will need to click on the create account button:
You will fill the Name, About, Current Balance & Account Type field in then click the Save button.
You have now created an account to be used in expense or subscription. You can now see the account in the Accounts home.
You can now click on your account to view it.