It can be hard to determine how to make a mobile friendly website in Xara, so this guide has some resources linked aimed at providing help at what should be encouraged and avoided when creating mobile variants.
Please see this guide on how to create a mobile variant in Xara.
This guide from Google highlights some common mistakes when designing a mobile site
When you create an object, it will only appear on one variant only. In order for it to appear on other variants, you'll need to share it. Please see this guide on how to do so. The templates that have mobile variants normally have all their content shared between variants, so changing one will affect the others. Please note that some objects can't be shared (for example navigation bars) due to technical reasons so these are copied instead.
You can use this test to see if you website is mobile friendly.