You will want to create a new machine by going to the main tab on the left and then clicking on it. Click on create a new virtual machine.
You will want to click on reactos as the operating system to install.
Then click on next and use all the defauls. ( note you should have about at least several gigs os space on your hard disk to do this.)
It will say image created and go back to the original window.
You will want to go to the reload optical drive on the lower left side.
You will click on the little cd icon.
Change to the directory where you extracted the cd
Choose the ReactOS-LiveCD.iso and press the open button.