It should be able to play those format by default. Just do a File --> Open and point to the file you wish to play
or you can just control-click on the file you want to play then choose Open With > Quicktime Player..
yup, i now make it a practice to drag the file to the player icon on the dock. i find it very....umm.....Mac. oh, you can also try to get the VLC player. it'll play almost anything. and it's free. and you can amp the volume with it in case your Mac has a weak sound (my MacBook has weak audio, so VLC helps a lot). peace out!
You can actually boost QuickTime Player's volume by hitting shift-up arrow multiple times while the file is playing. As far as I can tell, it increases the volume to VLC levels.