Upshifting and Downshifting

I am very interested in this topic but I can't follow all the terminology used. Can someone translate for me into english ?

What does slip the clutch mean exactly? Is that the same as feather the clutch?

And can someone clarify this statement? Clutch-move into 1st and move towards first. Is he trying to say something about shifting up into 1st and down into 1st? What is reduce shifter travel when clutch is disengaged mean? Is he just saying when the clutch is pressed in don't move the stick between gears alot?

Any wisdom on sitting at a stoplight on a slope with cars jammed in behind you and trying to avoid the car from rolling back?

Thanks in advance.