The original model used 120 roll film and had a 60mm fixed aperture lens. Later models used both 110 and 35mm film but kept a wide to normal lens.
Today, Holga makes plastic, fixed aperture, manual focus lenses for various digital cameras. While the models for some digital cameras retain their wide to normal field of view, the models for Nikon, Canon and some other cameras retain the original 60mm focal length which is a short telephoto on the crop sensor models for which they are designed.
You can read this and other information about Holga cameras and lenses on Wikipedia here. Here are images of the original camera and the current lens for Canon DSLRs.
Here are some examples I made recently beginning with the familiar bridge scene. While an aperture of f/8 is claimed on the lens, the aperture appears to actually be much smaller. Some reviews estimate the aperture to be approximately f/22. By the way, the lens costs $23.99.
The only way to really use the lens is in live view mode where the LCD brightens the scene so you can magnify the view to manually focus the lens then return to normal view to compose. It's not a quick process.