Arabic is written from right to left. There are 18 distinct letter shapes, which vary slightly depending on whether they are connected to another letter before or after them. There are no "capital" letters.
The full alphabet of 28 letters is created by placing various combinations of dots above or below some of these shapes. (An animated version of the alphabet shows the correct way to move the pen). The three long vowels are included in written words but the three short vowels are normally omitted – though they can be indicated by marks above and below other letters.
Although the Arabic alphabet as we know it today appears highly distinctive, it is actually related to the Latin, Greek, Phoenician, Aramaic, Nabatian alphabets. Other languages – such as Persian, Urdu and Malay – use adaptations of the Arabic script. The numerals used in most parts of the world – 1, 2, 3, etc – were originally Arabic, though many Arab countries use Hindi numerals. The following four lessons (part of the Babel course) give a fair idea of what is involved in learning to read and write Arabic.