If it's a language paper then basically you we will be asked to produce a piece of writing ranging as wide as anything from a letter, newspaper/magazine article, short story to a leaflet.
Basically though, with most of them you will have to think of a subject you feel strongly about and od one of these three...
Write to persuade.
Write to argue.
Write to explain.
Then you have to use the correct type of lexis/syntax and other techniques to suit the type of subject and what you are trying to achieve (out of the three above).
Is this A-Level or GCSE by the way?