Choose the right simulation environment at the beginning. Do explore HFSS examples. There is bound to be some CPW you can exploit. Look for the setup, or simply "Save As" a new file, and trash most of the example, keeping only the ports.
You can then change the substrate and CPW dimension parameters to suit yourself. Maybe just construct a simple test line with a little stub set between two ports, just to quickly check you get the S-Parameters OK.
I know it seems a little counter-intuitive, but CPW is Co-Planar-Waveguide. It can be fed from a waveguide port. So is microstrip. Even coax, so wrapped around itself it can only have a radial electric field, and supports TEM exclusively, can be fed with a waveguide port stuck on the end of it. Discrete ports, I think, force a voltage function between points on the track underside and to nearby on the groundplane, and you have to specifically define those points. Discrete ports are very useful, but you have to know what you are doing, and I do not think they are likely best when driving CPW.