Like in a real Unix terminal, the command is ls (LS, as in LiSt) - you can see the explanation in the "help" command. :)
Also the bracketed text is meant to be an example - you shouldn't actually type in the brackets. So an example command for listing the contents of a directory would be:
ls /Alex/Applications
And an example for executing a program would be:
./Alex/Applications/Gem_Writer.play
Hope that helps!