Most cover only the penis, leaving the testicles bare.
The length does not necessarily signify the social status of the wearer, or the size of the penis inside.
Some stick straight up, tied in place to emulate an erection.
The most commonly used gourd is the calabash (lagenaria siceraria). They are hollowed out, worked to the appropriate shape, and then dried.
Smaller sheaths are used for everyday purposes. For ceremonies, they can be as long as you want them to be.
Penis sheaths are used throughout Melanesia, and also in tropical regions of Africa and South America. Here Siko Nathuan, head of Vanuatu Island, poses with 18-year old British student Marc Raynor, who became the stand-in for Prince Philip during his birthday celebration. They're wearing straw penis sheathes.
The photos all show bare testicles, so I can't show them here. You can see them on Tales of West Hollywood.