Follow the procedure in the linked Guide. After clicking the blue link for New custom tax code, you will see a dropdown box for the tax rate. By default it shows 0%. Click to pull down the menu and select Custom:
Another dropdown box appears, in which you should select Multiple rates:
Now you see two lines for two components:
For your information, while you can create multiple tax codes for different situations, you cannot apply more than one to a line item. If, like many US jurisdictions, you have a multi-component sales tax, you should read this Guide:
https://forum.manager.io/t/working-with-multi-component-custom-tax-codes/7171