To use RTWTools you will need a copy of ENVI - one of the standard remote sensing software packages.
Download the latest release of RTWTools from here.
Simply unzip the file you downloaded and copy the
RTWTools.sav file to the ENVI
save_add directory. This will normally be somewhere like
"C:\Program Files\Exelis\ENVI51\classic\save_add" for ENVI 5.1 or
C:\Program Files\ITT\IDL708\products\envi48\save_add\ for ENVI 4.8.
Start ENVI as normal, and you should have a new RTWTools menu at the far right-hand end of the menu bar. You'll find all of the tools categorised underneath that. The interfaces to the tools are fairly self-explanatory, but if you need any help then just see the documentation.