Here is how some of the cheapest electric toothbrushes from Amazon works straight out of the box:
https://www.amazon.com/stores/Oclean

This is the Oclean Air electric tooth brush, which is now being succeeded by the Oclean Air 2 with more color choices.

In order to start it up for the first time, it usually has to be charged up.

You’ll be informed by the built-in voice what status the toothbrush is at, for instance if it needs charging. It charges by simply setting it atop of the magnetically attaching charger.

After a short charge, it can be used immediately, at 4 different vibrating speeds.

Oclean electric toothbrush