Only way I can describe it is you get more length and expression with each stride, horse tracking up or over tracking.
It feels completely different to them motoring on, with a definite feeling of suspension which comes from a push from the haunches
I only just started really getting it with Safi just before she went to Chelle's for the year. It was still a little rushed and onward bound, but the foundation was there to really work on.
Both my instructor and the judge that saw her first few dressage tests felt that Safi needed to be really pushed on to release herself...not a classical method by any means - Kate had us careering round the school until she "let go" - but it did produce results, which we then started to work on refining.
I'd worked with it on the lunge as well with the verbal cue to trot OUT, which I also used ridden till she got the idea.
More detail, pictures and a short video clip are
HERE, on the video she produces some nice strides along the second long side.