Wherever you are, if Wi-Fi is available, you will have the possibility to use a large amount of datas without any cost. If you do not need your Wi-Fi, you can (and should) deactivate it to save battery. If there is no connection to Wi-Fi, you need to turn it on in order to search for it. You can turn on Wi-Fi over the quick bar, or over the settings.

Android 10 | EMUI 10.0
Turn Wi-Fi on/off -  Open the  settings
Turn Wi-Fi on/off -  Tap on  Wi-Fi
Turn Wi-Fi on/off -  Activate or deactivate  Wi-Fi
  1. Open the settings
  2. Tap on Wi-Fi
  3. Activate or deactivate Wi-Fi

Huawei Instructions