What is the couch to 5k

I see others talking about this and when I try to get information there seems to be a fee for someone to tell you how to get started. Anyone one have some information they can share?

If you google "couch to 5k"you will see the plan.  it is free, and it looks pretty good to me, but I think I need to lose more weight before I try jogging on these knees

Thanks I will take a look at that!!!