[زيد الهلالي]

The video you have placed here is not for Parallel, but for Virtual Desktop rather. I can also see the user of this video is on a Mac mini with 1GB RAM only

you shouldn't worry about RAM, although more is better, but to answer you question… well Windows window on your mac is treated as a normal Mac window - ideally to switch from program to another ie. toggle - all you need is to press and hold command button and press tab button, this will bring another window to front