The official guide asks for a letter, or a message for a forum, an email or a blog, written from a short text you have read: a note, an advert, a letter or a post from an email, a forum, a social network, a blog or a magazine. The task tests whether you can produce a simple, cohesive informative text from your reading of a short one.
Each task gets a holistic rating and an analytic one, and the holistic rating counts for less of the final mark than the analytic one. The analytic scale has four categories: fit to the text type (Adecuación al género discursivo), coherence (Coherencia), accuracy (Corrección) and range (Alcance). In band 2 for fit to the text type, a letter keeps the basic conventions of its genre, such as the opening and closing, and develops nearly all the points clearly, though one may be missing or thin.
The lesson on writing task 1 gives the full method, a word plan and a worked reply.