Find a friend, relative, or co-worker with a computer that uses an operating system that you don't usually use (Windows, Mac OS, or Linux). Try out the operating system, and observe how it works compared with the operating system that you normally use. Pick the 4 or 5 things you do the most and use those in your comparison. Some examples might be organizing files, creating documents, accessing the Internet, using e-mail, uninstalling software, etc. Do not compare two different Windows systems (for example, Windows 8 and Windows 10).
An alternative to using someone else's computer is to create a "live CD" that lets you run Linux from a CD without installing it on your hard drive. To do this, you need a recordable CD drive and CD burning software like Roxio. Refer to the directions for Creating and Using a Live Linux CD.