A masturbation sleeve is a sex toy for guys. It’s an object into which a guy inserts his penis, designed to simulate intercourse or a blow job.
With some simulators you have to move the penis in and out (or move the object back and forth over the penis), but you can also buy them with a pump for suction feel, a rotating tongue housed inside or with a vibrator stimulating the penis.
They come in a variety of styles, colours and materials. Some are made in a tube shape; others have the shape of a vulva, mouth or anus. They can be made of jelly, latex and silicone.
The more expensive ones feel like human skin. Some are closed at one end, while the ones that are no more than a jelly rubber tube are open at both ends.

How to use it?
See also: sex doll