leg workout

I am reading about the 666 leg workout which is 6 sets of deadlifts, 6 squats and 6 cleans. My question is does it have to be in that order or do I alternate? Also how many reps do I need to do during those 6 sets. And final question for someone who is only been lifting for 2 months would...

Anyone heard of decline ham extensions? Ive heard they are a very good exercise for building the leg muscles..but has anyone used them before? Feedback will be much appreciated.