Sometimes, you don't have an icon available for opening a program.  You can use the Run command to launch a program instead. 

In the Computer Literacy classes  you use the Run command to launch the Telnet application from your home computer so that you can reach some of the computer networks on campus.  Here's a picture of what the Run command looks like.

By the way the only space in this whole sequence is between the exe and trex2. 

You won't have much opportunity for using the Run command but it is a useful option to keep in the back of your head.