By default, every Account has the "Standard" Account Type assigned to it. You may want to not use it, but you would be missing out on a feature that can be pretty powerful.
After reading this article, you will know what Account Types are and how they can be used.
Let's get you started
Where can you find the information about an Account Type?
The Account Type can be seen at two different places:
From the list of Accounts:

From the Account Record itself:

What are Account Types?
Account Types allow you to distinguish between your different Accounts, generally by level of partnership and/or commitment to your organisation.
Please note that an Account can only belong to one Account Type. It is therefore crucial to think about this classification and how you want to use it. If you need to manage several memberships for a single Account, we recommend that you use the concept of Groups.
What are they used for?
Account Types can be used in different situations.
For marketing purposes, you can easily filter those Accounts and their Contacts based on their Account Type.
But the main purpose of Account Types is to be used to create sales rules on the Portal for Tickets and Hospitality (Formulas, Packages)
This can be set up when you are on the Calendar item page.