Heres how I extract files, in 100% detail
1. find the folder WinMPQ is in, and run it.
2. click on File>Open...
3. find the MPQ you want to edit, for the default you should load StarDat.mpq, BrooDat.mpq, or patch_rt.mpq
4. right-click on a file, tell it to Extract, then select a folder and press OK
5. close WinMPQ