What are the main functions of the electric bike computer/display?

GPS functions:GPS will only be available on the cheapest (basic) bike computers. Monitoring the Global Positioning System (GPS) underpins a variety of data functions, including distance, speed, elevation, and navigation. For fast, accurate tracking, the most sophisticated (most expensive) units connect to multiple GPS satellite systems. 

Cycling functions: Most units offer baseline data like speed and distance. Advanced units track things like cadence, elevation, and power. The addition of special sensors to monitor key data improves accuracy, and many bike computers are sold as a bundle with those sensors. (Bundle prices are cheaper than buying items separately.)

Wireless technology: In the past, "wired vs. wireless" was an important distinction, but almost all bike computers now communicate wirelessly (with a power meter, a phone, a fitness tracker, or your laptop). Since most work with many communication protocols, including Bluetooth, this is not likely to be a deciding factor.

Navigation: More affordable units provide basic tracking and alert you when you’re off course. With the most sophisticated units, you can enter a destination and receive turn-by-turn directions. Basemaps for navigation systems are also different, with the best ones found in the top-tier units.

Mountain biking functions: The biggest benefit of this feature is connectivity with Trailforks, a leading app that provides trail information and navigational data. Mountain bike metrics include jumps, air time, and flow (the smoothness of your descent).

Display quality: Display quality correlates with price. The most affordable units have black-and-white displays, whereas the most sophisticated ones have color touch-screen displays. There are many bike computer apps that allow you to customize the display, including what data is displayed and how it appears.

Heart rate monitor (HRM) functions: These provide cardio and training data on par with the most sophisticated fitness trackers. To feed heart rate data to your bike computer, you'll need either an achet strap or a fitness tracker with a wrist sensor.

With these devices, you can monitor your health at any time, and riding an electric bike will make you healthier.