Understanding PATH$ variable

[Richard Owlett <rowlett@cloud85.net>]

I recently downloaded a python script which uses some custom helper 
scripts. The scriptS are provided as zip file. The instructions were ti 
download to chosen directory and un-zip the file.

The launching instructions were to do
   cd /path/to/script
then
   python script.py

That *WORKS* as advertised.

I thought I could "simplify" my life by doing
   export PATH=$PATH:/path/to/script
and then launch by doing just doing
   python script.py

That FAILED to find script.py .
May I be pointed to a complete explanation of the use of the PATH$ 
environmental variable.
TIA