Those of you who are Macintosh users may find the use of the PDAS programs a bit strange. You have to remember that these are legacy programs written for a command line environment. If you try to launch the application by double-clicking on it in Finder, you may be distressed when you get an error message.
In Macintosh terminology, these are 'console applications'. To run a program, you first launch the Terminal program. You will find it in Utilities under Applications. After launching, you will have a nice blank window open on your screen ready to accept commands from the keyboard. Now, if you have never worked from Terminal, you have a bit of work before you. I would suggest reading a beginner's guide to OS X on the topic of Terminal. I like the book by David Pogue, called Mac OS X, The Missing Manual. Refer to Chapter 15, 'Terminal, Doorway to Unix'.
If you are somewhat comfortable with the concept of using Terminal, then you launch your application by typing its pathname. By pathname, we mean the name of the program and the folder where it is located. For example, on my Mac, I have all the CD-ROM files in a folder called PDAS. So, for example, to launch panair, I would type
/Users/ralph/pdas/panair/panair.mac
and I would get the prompt to enter the name of the input file. If it is in the current directory, then you simply enter its name. Otherwise, you type its complete pathname.
One thing you need to learn right away is how to change directories and to be aware of the current directory. You need to understand the commands 'cd' and 'pwd' and be able to keep track of where your files are. Many of the programs write an output file in the course of execution. This always goes into the current directory.
If you have used DOS or command windows under Microsoft Windows, you may be accustomed to the convention that applications in the working directory may be launched by simply typing the name of the file. In Mac OS, this doesn't work. For example, if you are in the folder that contains panair.mac, the Panair application, you must indicate this by using the command string
./panair.mac
to launch the application. The single dot is an old Unix convention for referring to the working directory.