Fusion, Parallels (and Virtual Box, which is free) are software that lets you run another operating system within the main machine operating system, so called virtual machines. On a mac you start up OSX then run the virtualising software, and that will start the guest OS.
Bootcamp comes with OSX, you will need a copy of the guest OS as well. If you want to go the virtual route you will need a copy of VMWare Fusion or VirtualBox, etc as well as the guest OS.
Virtualising is more versatile, but is more demanding of hardware, especially memory. I run Windows 7 under Fusion on this iMac and JRiver doesn't work satisfactorily, because it's an old core 2 duo with only 4G of ram. It should work OK with a modern mac.
If you are using this machine only for JRiver, I would use bootcamp and boot straight into windows. That will make best use of the hardware and be simpler to get going. In fact, I've just bought a mac mini to replace my main JR video player and use bootcamp to run W7.