I'm going to show you how to fill a pastry bag. Here I have a plastic pastry bag. They also come in canvas. This one is a little too big for my taste, so I'm actually going to cut it down so it's easier to handle. Now that it's a more manageable size for me, I'm going to put my coupler in. This is called a coupler. It comes in two pieces. I'm going to put the larger part in first, right to the tip of the bag. I'm going to push it until I can see where I need to cut it off. Just snip the end and you push it through. You want it so that when you're pushing on the bag it doesn't pop out.
Then you're going to take one of your tips, this is a star tip, and just place it right on top. Then you're going to take your second half of your coupler, put it on, and just screw it right on. There you have your tip. Then I'm going to open it up and create a cup, and then cuff it around my hand like this like I'm holding a cup. I'm going to do about half way.
Then I'm going to add my frosting. With this hand I'm going to take my frosting with my rubber spatula and just put it inside. And with this hand I'm just going to grab it and pull so that the frosting goes right in. I'm going to add a little bit more. You don't want to add more than half way so that when you close it it doesn't come spilling out the top. Now that I have it in there, I'm going to shake it out, grab the top, and push the frosting to the top. I'm going to twist it so it doesn't come out the top.
Before you pipe anything, you're going to squeeze a little bit out just to get that air pocket out so it doesn't spill all over the place. That's how you fill a pastry bag.