You open it up, then open up the Warcraft3.mpq or the expansion MPQ if you want the TFT units, models etc.
Then at the top you'll "Extract" you can use that to export the files. You can also drag and drop I believe from Ladik's onto file explorer or your desktop or wherever. Boom, that's it, you've got the file.
CASC is only for later patches, if you have older patches with MPQs then MPQ editor is fine. I have both. There's a CASCviewer online
here.