You add a jazz article to articles already present.
Your money adds to the donation money already given to the tsunami victims.
Something that Ouisch mentioned adds to the already known factors in global warming.
Your post contributes to this forum, as does my reply.
"Contribute" means "to play a part in something by giving/adding to it". It doesn't have to be positive.
"Air pollution has contributed to the rise in cases of asthma". This means that other factors are causative, and probably more important, but that air pollution has 'added' something to the rise in cases.
Student or Learner