(Obviously you also need a copy of the Hitran or Geisa line parameter databases)
Save the package at some convenient place and unpack it: tar xvfz lblod4esas.tgz
Ideally add the bin directory to your system search PATH
If you are reading user guide's etc: in your browser open the index.html file in the doc directory;
Otherwise just extract line parameters from HITRAN and GEISA, then compute optical depth via cross sections by lbl2od