HSM Express is a free cam software that can be used inside of solidworks. It is basically the same program that Fusion 360 already has built in. I have used both and like both, but to be honest, I try to use Fusion 360 for all my cam work now. It just seems to flow a little better. As for post processor, use the Fusion 360 post that masso provides if using Fusion 360. If using any other cam program, use the standard Mach 2/3 mill post.
If you are not familiar with CAM packages you will need to learn how to use them in order to create the G-Code program that runs the MASSO control. The CAM packages automate the selection the tools, adjust feeds and speeds, as well as the various setups and operations need to prepare the program. MASSO works with most Mach 3 post processors that come standard with CAM programs. Just make sure to enable the options for Optional Stop, G28 Safe Retracts, and use M6. Also make sure that the Radius Arcs option is disabled since Masso does not support this type of code.
I also suggest that you go to the NYCCNC web site to learn the basics of preparing your CAM program and how to machine parts. Their video library an excellent place to lear how to work with Fusion360 and provides a ton of tips and tricks to help you get started.