1. Click Settings on the Navigation bar and select Payments & Taxes from the drop-down

2. Click on Add New Tax Type

3. Fill up the details and click on Add to finish adding the new Tax type

Name : Specify the type of Tax. Ex: Service Charge

Rate(%) : Tax Percentage. Ex: 5.0

NOTE: To assign the Tax type to a particular product, please refer the following link: How to assign a Tax type to a Product?