You are legally required to include a terms of services page within your website where you describe the terms for your shop. Your customers should also accept your terms before making a purchase. The mono tool has you covered on this, you just need to paste the link of your Terms page into the shop settings.

A terms page doesn't necessarily have to be a part of your main menu but it should be easy to find. A good place to link to it would be within your site footer. The actual page should be kept simple and to the point with less focus on the design but more focus on the headers and content underneath.