Arabic belongs to the Semetic group of languages. Other living languages in this group are Modern Hebrew (as spoken and written in Israel), Amharic, and other spoken languages of Ethiopia, Aramaic dialects as spoken in parts of Syria, Iraq, and Malta. Among the Semetic languages that are now dead, there is Biblical Hebrew, Akkadian (spoken in Babylon and Assyria) and Syriac (a major language of Christian communities before the rise of Islam).
The primary characteristic feature of Semetic languages is their use of root consonants which are usually composed of 3 consonants and occasionally 4 consonants. By adding suffixes, prefixes as well as changing vowels within these consonantal roots, the majority of nouns, verbs, adjectives and adverbs are formed. For instance Arabic names such as Mohammed, Ahmed, Hamdi, and Mahmoud all have the same 3 root consonants of H M D which relate to praise such as praiseworthy, highly praised, etc. As another example, the consonantal roots S L M refer to peace. Derivitives of this root are salam (peace), Islam, Muslim, salaamat (safety), asalama (to submit). Finally, if you are ever going to use an Arabic dictionary then you will need to be familiar with the consonantal root system.
The suffixes, prefixes and vowel changes that can be applied to consonantal roots are based on specific patterns which provide the various differences in meaning for a given consonantal root. This is a help in learning vocabulary and partly compensates for the difficulties arising from the lack of any common ground between Arabic and other European languages.
Arabic is usually classified into Classical Arabic, Modern Standard Arabic (MSA) and Colloquial Arabic. Classical Arabic is the language of the Koran as well as the great writers and poets such as al-Mutanabbi and Ibn Khalduun. Modern Standard Arabic is that which is used in newspapers, radio, news shows. It varies in idioms and vocabulary from the Classical Arabic of the Koran but the differences are minimal compared to the changes in the English language that occured between the time of Chaucer and present day. This is because Classical Arabic was revered as the vehicle of Allah's revelation in the Koran and was therefore not permitted to change to any marked extent. Modern Standard Arabic is taught in schools throughout the Arab world and thus becomes a sort of lingua franca that allows those who speak different colloquial dialects to understand one another for the most part. With regards to the colloquial dialects there are many differences between them and Modern Standard Arabic yet the vocabulary, grammar and pronunciation differences of these dialects can be learned quickly if one has a good base in Modern Standard Arabic.