Freezing

So every time I see a video about how to improve my gameplay, it says something along the lines of learning how to freeze the wave. I have absolutely no idea how to do this, and after getting someone to explain it to me, I still have no idea what I have to do to freeze a wave. The most common time I hear when I'm laning against a Nasus is to poke him down, and to freeze the wave. Now poking the Nasus is pretty self-explanatory, but no matter what the wave always ends up near their tower, and then I get ganked, withered, and then I die in the 2v1. And this happens over and over, because I get camped by the jungler. No amount of wards save me, as he withers me, and as I'm getting stuck on my minions, I end up unable to get away before the jungler arrives, and even if I did I would get dove immediately. Then I got flamed for not freezing the wave, pushing up when I know I'm getting camped, etc. In my defense, I felt that zoning Susan from getting stacks was more important than sitting at my tower because I'm getting camped, because if I let him get stacks, the game is pretty much over. So I have two questions: 1.) How do I freeze the wave? 2.) How do I recognize/break a freeze when my opponent is freezing the wave?

If I can learn to freeze the wave, I won't have to overextend myself and die due to creep block and jungle camps.