If you are talking about KYG_Invoicing, then
First fill the details by clicking on Your Comapny
Then click on Add Product and add rental income as product
Then click on Add Party/Vendor and fill details of your payee
Once this is done click on Create Invoice a new window will open. Fill the details and save it. Your invoice is created.
To take printout, click on Invoice List, list of all invoices will be generate. Click on First button Action column. A new page with invoice will open, you can take print out directly from browser window.