I recently downloaded and the Crescendo (<) and the Decrescendo (>) aren't working
AFAIK, MuseScore still doesn't translate many musical ideas into MIDI. Volume markings are among these.
Correct. The markings "work" in the sense they are meant to work - they appear on you score. MuseScore is primarily about producing printed notation, not playback.
But if you want to get these symbols to playback, see the Plugins menu at right of this oge and check out the crescendo plugin. You have to apply it manually, but it does work pretty well. Still, you'll find that if you are thinking of MuseScore as a playback program primarily, you'll likely be disappointed, as there are other lmitations too not so easily worked around,
Crescendo and descrescendo playback will work as of next MuseScore release, i.e. MuseScore 2.0.
Apps and the API