Welcome to the Community, @fidaghazi619. I can assist with setting up expenses for 2018.
Intuit offers multiple tutorials to help users with QuickBooks Online. I'm including one of these resources which can guide you on setting these up: Manage Expenses.
Additionally, since you're needing to generate a Profit and Loss report, I recommend the following article which contains insight on customization options: How to Customize Your Profit and Loss Report.
These links are a good place to begin.
Should you have questions or need anything, please post a comment below and I'll get back to you. Best wishes.