Cartomizers generally come delivered with a frosted looking, soft plastic covering both ends of the carto. These are called "condoms" in the trade, and some people use them for filling their cartomizers with
juice via the "condom method of filling cartomizers". Look it up on You Tube.
The is also an either hard or soft white plastic ring in the top of the cartomizer, which some people call a "doughnut". This piece is just to insure nothing gets into the cartomizer until it is ready for use. It may be removed with any small tool like a paper clip and thrown away.