Alif, ﺍ, at the beginning of a word represents a short vowel sound (a, i, or u), a long i, or an ay sound.
Alif madda, آ, is used when a sustained 'a' sound occurs at the beginning of a word.
The next character has two forms. The joined form, بـ, is used when the character is followed by another character. The full form,ب, is used when that character appears by itself or at the end of a word. Remember that Arabic is read from right to left. Arabic characters should be written form right to left as well.
Most Arabic characters both joined and full forms. Here are some more characters with both forms.
Alif in the middle of a word represents a more sustained 'a' sound. Short vowels aren't represented by a letter when they appear inside a word. Alif is one of the few letters that joins with letters that precede it. It never joins with a letter that follows it.
Some of the following characters have both full and joined forms. Others just have one form. The first letter, ج, is pronounced as a j everywhere except in Eygpt where it is pronounced with a hard g.
ع and غ have four forms. One form is used when the letter starts a word, one when joined with both the preceding and following character, another when at the end of a word and joined to the preceding character, and finally a form used when it isn't joined with another character.
In middle of a word, wow can represent the long vowel u or the vowel combination ou, ow, or w and at the end of a word, the long vowel u and sometimes ow.
The joined form of ya,يـ, ي is another example of a tooth. Ya is pronounced as the consonant y at the beginning of a sentence, long i, in the middle, and long i at the end.