Thanks for sharing your concern with us, alimurtazamaxim-.
You can only customize transaction forms such as invoices, sales receipts, and estimates on the online version of QuickBooks. Thus, adding terms and condition section on the Purchase Order template isn't available.
I've included an article that will guide you in designing your invoices and sales receipts to boost your business' brand: Customize sales forms.
In the meantime, I'd recommend visiting our blog for the latest happenings, feature developments, and product updates: Firm of the future. It also includes the link for our resource center where you can find tips on how to effectively manage your business's growth.
Additionally, you can pull up reports (i.e., Open Purchase Order List, Open Purchase Order Detail, Purchases by Product/Service Detail, Purchases by Vendor Detail) to effectively monitor your PO transactions in QBO. Just go to the Expenses and vendors section from the Reports menu's Standard tab.
You might also want to visit our QuickBooks Online learning guides for tutorials and webinars about the product.
Let me know if you have other concerns about purchase orders or inquiries about managing vendor transactions in QBO. I'm just around to help. take care always.