This page explains how to install the Wolfram CDF Player. This is a piece of free software I'll use this semester to provide interactive demonstrations of concepts from class.
Go to this site and download the installer. Unfortunately, it asks for an email address. I haven't received much junk mail from giving them my address, but there doesn't seem to be a problem with giving them a bogus email address either.
Next, run the installer. On Windows and OSX, the CDF player may or may not work from within your browser. If it doesn't run within your browser, you should still be able to start the program as an application and use it that way (this is how I prefer to use it).
To test your install, download this demo, and try opening it within Wolfram CDF Player. You will probably need to press the button that reads "Enable Dynamics" (this warning pops up depending on where you saved your copy of the demo --- you can safely ignore it). If you can interact with the graphs by sliding the bars, you were successful.
If the above steps don't work, I'm happy to help you in office hours.