Omniglot is an excellent resource for learners of just about any major world language. Simon Ager has put together an exceptional amount of information about the systems used to express language in the written form, complete with images, explanations and audio samples.
There are two main types of written Arabic:
1. Classical Arabic - the language of the Qur'an and classical literature. It differs from Modern Standard Arabic mainly in style and vocabulary, some of which is archaic...
2. Modern Standard Arabic - the universal language of the Arabic-speaking world which is understood by all Arabic speakers. It is the language of the vast majority of written material and of formal TV shows, lectures, etc.