Adding an awning to your your van or RV can be an excellent way of giving yourself more room, by giving you an outdoor room/space to socialize or hang out in even in rainy weather.
Awnings can be polarizing; many dwellers report that it's the single greatest thing that they've ever added, while others have said that after adding it that they barely use it.
Your mileage may vary.
Low and medium roof vans usually need an awning that is mounted to the roof, to clear the side door opening. Custom mounts can take advantage of the factory roof rack mounts, or they can be attached to an already existing roof rack. The Fiamma F80s is an example of a roof-mounted awning.
High roof vans typically use a wall-mounted awning to the side of the van. It's possible to use a roof-mounted awning, but the height of the vans can make them difficult to operate. FarOutRide has probably one of the best installation guides on how to install a side-mount awning to a Transit, but similar brackets are available for Promasters and Sprinters.
Depending on your budget and what type of vehicle you're attaching it to, there's a few different styles of awning.