This is the Modern Standard Arabic alphabet or adjab. Arabic characters are most often written and typed in a cursive format. As such most of the characters have a slightly different form depending upon its placement in a word. There is an isolated form which is the basic form, it is used if the character is to be written on its own. The initial form is used when the character is the first character in a word. The medial form is used whenever a character is used in the middle of a word between two other characters. The final form is used when the character is the last in the word. Arabic is written from right to left and so the first character of a word is on the right not the left as in English and other Western languages. Arabic may been seen written vertically on some signs, in this case the isolated form is used.
Arabic makes use of diacritic marks to signify vowel sounds for most of the vowels. As you can see from the image below the diacritics add the vowel sound to the basic sound of the consonant that they are attached to.
Arabic uses a base 10 counting system like much of the world. The numbers used in the Western world 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 are known as Arabic numerals because they were first introduced to Europe from Arabic scholars and mathematicians, however the numbers used in Arabic are know as Indian numbers suggesting that they were adapted from an early numbering system originating somewhere in the Indian sub-continent. It should be noted that while words are written from right to left in Arabic, numbers are written from left to right.
Here we see the Arabic numbering system in three different dialects. The first is MSA (Modern Standard Arabic) followed by Moroccan and then Egyptian.