What you are trying to do is way beyond a simple explaination. If you have a bitmap picture such as a .jpg you have to trace the objects you want with the various drawing tools.
If you want to you can try Power Trace if you have Draw X3 or above.
If you just want to isolate the objects from the background you would be better off to use Photo Paint. You can remove the background with it but it is also to involved to try to explain here.
The best thing to do is to Google for tutorials on Corel Draw and Photo Paint.