To configure taxes, you need first to sign in to the Back Office.
After signing in, go to Settings.
Then go to 'Taxes'.
Then press 'ADD TAX'
... and name the tax.
Then input the tax rate
...and specify whether the tax should be included in the price, or if it will be added to the price at the counter..
Select the items to which this tax should apply.
Then press 'Save'.
Now taxes are configured, they will be applied for each purchase.