hey i cant seem to do this thing.....

If you extend the left or right edge, the clip becomes very unpredictable !!! isnt this supposed to slo-mo (lengthen the length of the clip) or speed up the track (shorten the clip)???

EDIT: ah ok, i needed to have CONTROL-LMBUTTON..........so how do i use velocity envelope WITHIN a TRACK to change the speed in ONE SEGMENT??

so how do i do slow mo on a section of a track without cutting up into little pieces into new tracks??

It is not the world easiest thing, you could Right clip the clip and go to properties and change the speed there then when you stretch the video it behaves in a more predictable manner.