With the mobile data function you can control data access over the mobile network. To use the internet outside of the Wi-Fi network, your mobile data need to be turned on. Also you need a correct APN to connect to the internet, although this will usually be configurated automatically. You can also deactivate mobile datas on your Huawei device. 

Note: You can also turn the mobile options over the quick settings over the notification bar.

Android 10 | EMUI 10.0
Step 1:  Open the  settings
Step 2:  Tap on  Mobile network
Step 3:  Tap on  Mobile data
Step 4:  Activate or deactivate  Mobile data
  1. Open the settings
  2. Tap on Mobile network
  3. Tap on Mobile data
  4. Activate or deactivate Mobile data

Huawei Instructions