Welcome to AndroidCentral Hopefully we can get you sorted.
Firstly, could you let us know what Huawei device you have?
Do you have a "App Draw" at the bottom of your home screen, it should be in the middle with 6 little dots inside it. That will open up all the Apps installed on your phone.
All you need to do then, is locate the calculator app and long press on it. You should be taken back to the home screen and can now drag the calculator app where ever you want.
OR
Long press on your home screen (in a empty space). You should get a couple options that appear at the bottom. Have a look for "Shortcuts" or "widgets". This should allow you to then select an app you want to add.