Windows runs on your Mac as a “virtual machine,” or VM. Parallels Desktop is a virtualization app.
Windows becomes a file on your computer. Parallels opens that file and tells it to pretend that it is a real computer.
You can start that computer, shut it down, put it to sleep (a.k.a. suspended), or wake it up. Also, you can look at it in a separate window, or full screen, or have the windows you have open on it appear as individual, discrete windows in your Mac environment.
Most of the time, you will have Parallels quit, and Windows suspended. When you open the Parallels Desktop app, you will be asked to resume Windows 7.
Then, when you are done with what you need to do in Windows, simply quit Parallels, and it will suspend the VM.
When you do need to have windows running, you should probably quit any other apps that you don’t need to use at the moment. Running Windows consumes a great deal of memory, leaving less room for other apps to do their job, which will result in the spinning beach ball.
As you would with any computer, if Windows is misbehaving, turn it off from the Start menu at the bottom left corner of the Windows screen. Parallels will make it obvious how to fire it back up.
I don’t do much to Windows after I install it, with three exceptions: I install Microsoft Security Essentials, and Google Chrome. I also run Windows Update, which you can find using the search blank in the Start menu.