A veranda is a covering that is placed outside of the home, usually onto the side of a building. They are often used to cover a patio or a decking area to give it some extra shelter from the elements. They can serve many functions, on top of simply looking great and potentially even increasing the value of your property.
A veranda tends to be a permanent feature, as opposed to something like an awning which might well be retractable. It is often made of glass, metal and plastic, giving good coverage and providing shelter within a garden setting.
By doing this, an awning is able to cover a lot of bases. It can be used in the summer months to give some shelter from the sun. It can also be used as the weather gets worse, offering shelter from occasional rain. You can even get verandas with sides that will prevent wind entering in the winter.