There’s several parts of a package design in Illustrator that all need to go on separate layers:
Outside edge– this is the line to cut after the package is printed out. Should be done in a bright color that contrasts with the design.
(Optional) Window– This also gets cut out along the outline, and is represented with a solid color such as cyan. This only applies to packages that will have a window cut out.
Bleed– This is the part of the design that extends 1/8 inch past the outline so that the design does not get cut off. Should be in a bright, high-contrast color.
Barcode– for identifying the item.
Folds– also should be in a bright, contrasting color. This is where the parts of the package get folded.
Glue– represented by small X’s. Should not have the design on it, as ink can affect the effectiveness of the glue.
(Optional) Perforations– Where the package will be easy to tear open. Also represented in bright, contrasting color.
Here’s how all the layers look together!