Professional chefs fill a piping bag holding it in one hand, as shown here. Another method is to pull the sides of the bag over the rim of a jug to act as a support.
Fit the nozzle securely, then twist the bag above the nozzle to prevent leakage.
Fold the top of the bag over your hand to form a collar; spoon in filling.
Twist the top of the bag, until filling is visible in nozzle, to clear air pockets.