You mean "mirror" modifier? There isn't such a mode in Inkscape. Wait, I take that back. Create your half object, create a "clone" of it, then flip it horizontally and position it beside the original. Now when you edit the original the clone will update.
i can't do that i have to make them as group and adding a new object to the group then regroup it is pain in the **s i think we need something like blender more advanced