A basic braid is simply a single braid down the middle of the head. It can start from the hairline, from the middle of the head, or down closer to the neck. The end is usually left hanging down, but can also be wrapped into a bun or tucked underneath the braid.
Basic braids are the most common type of braid. If the hair just above the ears is long enough to touch when being pulled back behind the head, the hair should be able to be put in a basic braid.
For more pictures of basic braids I've done, see the Flickr tagged set here.