Welcome to the forums,

First let's be clear here. Xara Xtreme is not Photoshop and neither is it a raster (aka: bitmap) editor. So clear your mind of the raster-mindset, it will help with your future questions

Xara Xtreme is a primarily a vector graphics illustration application.

To your question.
Removing the object from a white background depends very much on the image and the purpose for the result.

Most commonly the shape editor is used to 'cut out' (intersect) the object from the background. But there are a umber of different approaches depending on the intended use of the graphic.

But rather than me going through all this yet again, please make use of the forum search because your question has been asked many many times over.

Here's one result to help you along