They have applied what they know about the elements of art, the principles of design and the language of images. Now they will be trying to figure out what the work is about. Some abstract works are about, for example, colour. Some are about feelings.
Some art works are about social issues or cultural issues.
Other works are highly intellectual, and might not be as easy for us to know readily what the artist was thinking. The previous comments are an example of the sorts of topics students will be dealing with at the interpretation stage. The types of questions asked will vary with the type of image or work of art being discussed. For example, some paintings do not have representational subject matter. A question about theme would not necessarily be relevant for these works, but you can still deal with the question of why the artist created the work and what the content of the work is.