How much RAM does it need?Yes, that is how to get VMware Fusion for free - the process can be a bit convoluted. You still need a license, but it doesn't cost money.
VMware Fusion runs on a macOS system (the host) and creates and controls client virtual machine running other operating systems (e.g. old macOS, Windows or Linux) which use the same CPU architecture - typically Intel virtual machines on an Intel host.
Yes, the virtual machine macOS will run a bit slower than you might hope - mostly due to graphics being slower. If graphics speed (games) is important, you might do better with Parallels (which doesn't have a free license).
I frequently run High Sierra as a virtual machine on my Ventura 2019 iMac as High Sierra is the lastest macOS with reliable drivers for my Canon scanner. It is also able to run older 32-bit Intel Mac apps which can't run on more recent macOS.
You mention macOS (OS X) 10.6. I have virtual machines back to 10.6.8 Snow Leopard. But installing 10.6.8 is decidedly tricky because non-server macOS 10.6 is NOT licensed by Apple to run in a virtual machine (even on Apple hardware) and VMware attempts to enforce that. You also need the 10.6.8 installation media for which Apple charged. Anything more recent is fairly easy.
The virtual machine will need RAM for its exclusive use when running - hence problems for a host Mac with base level RAM.
Can an older MAS OS run on Parallels? I thought it was just for running Windows.
I have a 2009 Mini running OS 10.6.8. I have it cloned to an external drive. Would I be able to copy the cloned drive to VMware?