How to fill the frosting gun?

[TakataCheroki]

For some reason, I can't figure out how to fill the frosting gun that you use to decorate cakes. I can do fillings, and I can use the frosting knife, but I can't figure out how to fill the frosting gun. The little tutorials/tooltips aren't helping; I can't find what I need.

I've tried left-clicking, right-clicking, and pressing E on both the frosting dispensers, frosting container, and even the fillings jars but I can't get anything into it. I want to draw on my cakes, but I can't until I can fill the frosting gun.

What am I doing wrong?

[XTS]

They should be prefilled with white. To change a color, put down the decorator and pick up a dye jar (any color you want) then click the decorating applicator :D You can add more or less, add other colors. It's not flavor so much as decoration with those.

You can also change out the tips :D