Allorache

I am brand new to Designer and don't have a lot of experience with graphics programs. The first thing I've tried to do is use the knife tool to break apart images. I've read the documentation and watched two tutorials. I click and drag and either my line disappears; or the line is there but I can't move the part of the object that should have been cut. Sometimes when I click the knife tool I get a square box and it says "0 objects". I do not have a mouse. I have a laptop with a touchpad and I have a wacom tablet. I don't know if the problem is that I can't click and drag without a mouse?? And while I don't have much experience with graphics, I do have the Hatch embroidery program and I'm able to use the knife tool in that program no problem.