Go to the Invoice module then click on Estimates on the left menu or you can go to the Quick Add menu and click on Estimate Once you are in the Add Estimate page, please select the name of the Contact (someone you may be doing business in future) or ...
You can either go to Invoice module, then click on Invoices on the left menu or you can click on the QuickAdd menu and click on Invoice Once in the Create Invoice page, click to add a Customer if it does not exist, if the Customer records are there, ...