A shop vacuum, sometimes referred to as a wet/dry vacuum, works on the same principle as a regular vacuum cleaner, with only a slight modification in design. In practice, a shop vacuum extends the functionality of a traditional household vacuum cleaner with its ability to suck up larger particles, as well as liquid spills of the kind often found in industrial and workshop situations. It's perfectly fine to use a shop vacuum in your house, though the lack of finer pointed attachments might make it harder to pick up every small particle of dust and debris.
Most shop vacuums look like a trashcan on wheels, eschewing the more slender design of traditional cleaners in favor of a low, wide, cylindrical shape perfect for quickly disposing of big messes. The heart of the wet/dry vacuum system is an electrical motor that sits on top. As with other types of vacuums, this motor begins spinning when the device is turned on. Fan blades attached to the underside create a low-pressure condition which, when compared to the outside environment, manifests itself as suction.
The dirty work of a shop vacuum is achieved by a hand-held, tubular wand open at one end. Suction generated by the lower air pressure inside the vacuum is focused through the open end of the wand. The principle is the same as sucking a drink through a straw. Wherever you aim the business end of the straw is skimmed clean. Same with the shop vacuum. Depending upon the size and horsepower of your model, a wide array of liquids, dust and debris can be sucked into the innards of the device.
With a traditional vacuum cleaner, debris is collected inside a bag which, once full, is replaced. The air stream carrying liquid or debris through a shop vacuum flows over a round central reservoir that looks like a janitor's bucket. This wider area allows anything carried by the air stream to fall into the bucket. When it's full, it's a simple matter to release a few clamps, remove the motor assembly from the top and dump out all the junk you vacuumed.
The laws of physics decree a few truisms when it comes to wet/dry vacuum operation. For one, the stronger the motor and larger the size of fan blades, the greater the suction force generated. Most vacuums come with various sizes of attachments that can be placed on the end of the suction rod. A narrower attachment focuses the air flow and allows you to pick up heavier pieces of debris. The particular attachment you choose varies depending upon the job at hand.