Maya needs to know where your mel scripts are located in order to source and run them. When Maya is installed, it normally sets up a default scripts and plug-in directory for you. Under NT, this is normally in your winntprofiles?????maya directory. If you want to use other directories, you must setup the environment variables MAYA_SCRIPT_PATH and MAYA_PLUG_IN_PATH. With these variables set, you can have as many different locations for your scripts and plug-ins as you want.
I assume your script doesn't run because Maya doesn't know to look in My Documentsmayascripts.
You need global proc's for many different reasons. Any procedure called through a callback (like a button press, or a slider change) must be global so Maya can find the procedure to call it. If you are making a large mel project, you may want to have multiple files. The routines that are shared between the files must be global. I think what the scripting manual was trying to say was not to make ALL your procedures global by default. If you have supporting procedures that are only used by the other procedures in the same file, those don't need to be global.
Your variables will be whatever you define them to be, no matter if you have a local or global proc. Local variables inside a proc are local variables. Global variables must be defined with the keyword global in mel and therefore will be global. Global variables are global. You have access to them and their values at any time.
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