Not sure how to use this

I recently purchased one at a local thrift store. It doesn’t have the dongle, and I’m intending to use it with my Mac. (I don’t have a PS3.) I plugged it into the USB port using a USB mini B cable, and now I have no clue what to do or how to connect it, if it even will. All it does is flash green, and I can press a button at the top to light the whole controller up green. Can someone please help?