Once you have enabled Automatic eway bill, you will have option to generate eway bill when you are creating new sales invoice.
You might have to disable popup blocker for hisab.co, otherwise it may open only one PDF tab.
You can see generated e-way bill number under E-way bill no column in Sales invoice List page as well.
When you create sales invoice for same contact again, it remembers your previously added data and configuration. So if you now create sales invoice for above used Contact, it will have all your E-way bill configuration pre-filled. You can still change it if you require.
If you are facing any issues with this, please refer to troubleshooting guide.