Attach the stem to the flight stand base. The hard plastic of the flight stand will bond firmly with plastic cement, but you can also use superglue.
There are two sizes of stem; the standard practice is to use the shorter stem for helicopters and the tall stem for strike aircraft, to bolster the impression that they are flying at a higher altitude. But there's no reason you shouldn't use the tall stem for helicopters if you like how it looks.
Left: The stem attached to the base.