To get to the main menu where you can start creating transactions, just click the Plus icon. This is located in the upper right-hand corner of the Dashboard before the Search icon (magnifying glass icon).
When it's maximized, you'll see a menu to create transactions for your Customers, Vendors, Employees, and many more. I've got you a YouTube link for the video tutorials that you'll need when working in QBO: Video Tutorials for QuickBooks Online.
I'm looking forward to seeing you again in this forum if you need more help with QBO. Thanks for dropping by.