A portable canopy is essentially a tent without sides, just a top supported by poles. If you want to vend at a flea market or art show, you need a portable canopy. Other uses include providing shelter for picnics, outdoor receptions, or even a makeshift carport in climates where the sun can ruin your car's finish.
Portable canopies used to be fairly complex to erect, but in the past few years, the 'pop-up' portable canopy has become widespread. Based on the same principle as the collapsible umbrella, the popup portable canopy can be set up and taken down in a fraction of the time of a more traditional canopy.
The vinyl covering can be a number of colors, but most people choose white, because it's reflective; a darker color would absorb more heat and make the area under the canopy hotter than necessary.
You can buy a variety of additions to your portable canopy. It's probably a good idea to get one or two side walls. These can be stretched between the supporting frame's corner poles and provide shade or shelter from wind or blowing rain. If you are selling merchandise or fine art, protection from the elements is a necessity. For reasons that have so far escaped scientific study, it always seems to rain on street-fairs and outdoor art shows.
Side walls are also useful if you need to make clear to the public which side of your booth is the front; you don't want people walking behind your cash register. A wall in the back and a table for the register clearly defines a 'staff' area as separate from a 'sales floor' area.
Other amenities to add to your portable canopy include an awning to define your front door, and mesh walls that allow air in, but keep bugs out.
Portable canopies come in a wide array of sizes, with 10'x10' (about 3m x 3m) being the most popular. (Most street-fairs or flea markets sell space in 10x10 units.) A popup portable canopy of this size can easily be set up by two people.