Thank you for reaching the Community, 1R.
If you mean learning about customer topics in QuickBooks Online (QBO), you can visit this link where you can find tips on managing sales and customers: Topics about your company's income and customers.
If you wish to know the basics, you may also want to visit these easy-to-access articles, webinars, and video tutorials. This will help you in familiarizing the different tasks, features, and functions of QBO.
It'll be always my pleasure to help if you have any other questions. Just keep me posted in the comment section down below.