Hello Vanaheim,
Welcome to the Community. I'll be happy to share more info so you can continue to navigate the program with ease.
The program is designed to help you manage your suppliers. For recording suppler purchases, I encourage you to check out the following article that shows you how to: :Enter bills and record bill payments in QuickBooks Online.
For categorizing transactions, I recommend referencing this article: Categorize online bank transactions in QuickBooks Online.
For recording supplier credits, check the following article with more info on how: Enter supplier credits and refunds in QuickBooks Online.
For functions that go beyond the steps in the articles above I recommend consulting with your accountant to learn more about how to accurate handle the supplier transactions. You're welcome to ask questions in the comments below. I'm here to steer you in the right direction.
