throttle should come with the throttle tube attached - do not loose the little brass ferrules that hold the cables in place or you will be hunting for weeks on the floor looking for them

you will need to release some cable to allow you to remove the grip so you can get the ferrules out.
Undo the switch housing and remove the ferrules and slide the grip off replace with new grip put cables in put the switch housing back together ensure free rotation of the grip.
now over to the other side, remove the grip you may have to cut this off as its glued in place, get some fine sand paper and sand the remaining glue from the bar.
Get your hands on some extra firm hold hair spray, spray inside the grip and slide it on, leave for at least 12hrs to dry voila grip is held in place and is removable if needed with out cutting it off