It's a bit intimidating getting started, but once set up, e-tube is well worthwhile. It gives you a portal into the DI2 system on your bike and allows you customize the system to your desire. The best example is what we were talking about above - you can change the function of each of the six switches that are available to you.
To get started, you download the application to your cell phone and/or a laptop. In general, there's no real reason to run it on your laptop, with one exception: for some strange reason, you can only update the DI2 firmware on your bike using the laptop. For all other purposes, cell phone works best. For 95% of what you and I would do, you'll use the application on your cell phone.
To find and download the software, go to
https://bike.shimano.com/en-EU/e-tube/project.html (or just google 'etube'). Once there, you can download the application for Apple or Android.
Once you have the application running on your cellphone, you use bluetooth to link to your bike. I can help walk you through the steps if that would help. I'm no expert, except that I've been through the process.
The application gives you a graphic representation of all the DI2 components on your bike (switches, derailleurs, batteries, and so on) and lets you decide what function you want each switch to perform. That's how I discovered the existence of the two extra switches.