After creating your sales order, you can issue invoice from EMERGE.
Generate an invoice from sales order
To generate an invoice:
Click Orders > Sales Order on the main navigation panel
On the listing page, click on the sales order which you want to generate an invoice
On the Sales Order details page, click the Invoice menu on the top right corner > Quick Convert
The system automatically creates an invoice with all sales order items using system defaults. You can update the system generated invoice. See Updating Invoice
For partial invoicing as well as issuing a single invoice for multiple orders, see Partial invoicing & issuing a single invoice for multiple orders