How-To Fill A Pastry Bag
Holding the pastry bag with one hand while using the other hand to fill it can be tricky. Instead, do this:
Secure the frosting tip and coupler on the pastry bag. Place the bag's tip into a tall empty glass. Fold the bag's wide opening halfway over the glass. Use a spoon to transfer frosting to the bag. When it's three-fourths full, put the bag's sides up over the frosting. Lift it out of the glass, twist the open end to close and apply pressure to the bag as you happily pipe away.