Okay, I didn’t realize you were trying to create these things in CorelDraw. That isn’t a program I currently have installed, (or am familiar with - I ran out of time before getting into any CorelDraw tutorials) so I’m not going to be able to give you any quick specifics on how to fix it.
Having said that - you first have to convert any text into Curves before you can use it in the Shapes manipulations. @johnwills has a tutorial for it in the Matrix:
Another thing I picked up from what you typed above - you are using the Combine tool to try to subtract your shapes, and I’m pretty sure that’s not the correct tool from what I have been able to discern in CorelDraw. You need to be using the Trim tool under the Shapes menu. That seems to be the equivalent of the subtraction tool in the other 2D vector programs.
There are a couple of video tutorials linked in the Matrix for how to use them, and one on the difference in treatment between Combine versus Weld so you can see what’s happening.
See if doing those two things doesn’t move things along a little better. 