VMWare is free for this course. You should follow the installation instructions precisely, located at https://manual.cs50.net/appliance/2014/
Also, take note of the following (from the windows version of the instructions)
2.The VMware Software Center is set up like a store. On the "store front"
page, click on VMware Workstation 11. If you see both a free and a non-free
offering of the product, choose the free one. In the drop-down menu labeled
Choose a platform, make sure that Windows is selected. Click the Add to
Cart button, then proceed through the check-out process until you reach a
screen with a Start Download button. After a momentary delay, your unique
product key should appear in red on that screen. Copy that key into a place
where you keep software serial numbers and license keys. You’ll need it to
install Workstation 11 now and to reinstall it later if the need arises.
Mac instructions will be different, but you get the idea.
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