Hello again Sasan,
It's great to hear that you've been exploring the QuickBooks Community to try to find the answers you need. The article you've found is useful for when you're filling out your end-of-the year T2125 tax form for self-employment. If you're looking for help with categorizing your expense transactions in the program, however, it's not quite as helpful. I'll help you with sorting this out.
The article you've linked actually has a link to a CRA page that goes over the various kinds of expenses you might incur as a self-employed business owner. I encourage you to check it out to see if it helps with categorizing your expenses: Business expenses
If that doesn't help, I recommend getting in contact with an accounting or bookkeeping professional. These individuals have the training and the know-how to help business owners such as yourself. At QuickBooks, we have our Find an Accountant feature, which helps users connect with accountants and bookkeepers who know QuickBooks Online and QuickBooks Desktop. While we don't have one for QuickBooks Self-Employed, one of these individuals may still be able to help you. QuickBooks Online is the most closely related to QuickBooks Self-Employed of the two. Keep in mind, however, that you cannot add an accountant user to your QuickBooks Self-Employed account. Feel free to leave feedback for the QuickBooks Self-Employed product development team about this by going to the Assistant feature in product, typing and entering Feedback, and then following the prompts.
I hope that helps. I'm here if you have further questions.