- Enable tax. Whether or not taxes are included in each purchase.
- Display tax in shopping cart. You might prefer the customer not to be aware of the taxes that are applied to the order. In that case, disable this option.
- Base Based on. The customer can choose to have the product not delivered at the same address as the one the order invoice should be sent to. This can have a great impact on taxes. By default, PrestaShop bases its tax rates on the delivery address, but you can choose to have them based on the billing address.
- Use ecotax. The ecotax refers to "taxes intended to promote ecologically sustainable activities via economic incentives". It is a tax that shop owners pay in order to "feel the social burden of their actions". Learn more about ecotax on this Wikipedia page: http://en.wikipedia.org/wiki/Ecotax.
Once you have enabled the use of ecotax, all your products' back-office page will feature an "Eco-tax (tax incl.)" field in their "Prices" tab. You should fill that field with the exact value of the tax, which depends on your country's tax laws (it is probably based on the product's price).