The direction of Arabic language writing is from right to left except for sequences of numeral figures which read from left to right
In Arabic language there is no such thing as capital letters 
There are 28 letters  which all  are consonants but  ( letter alif, waw and Ya ) are used as  long vowels or diphthongs and also play a role as weak consonants

SHAPES AND GROUPS

Arabic letters may be divided into several  shapes or groups 
Various letters may have the same basic shape but are differentiated from other letter in their group by the addition of dots above or below a main shape  Consult table 
   

In Arabic there are two basic kinds of letters
   (1)  Connectors which may be joined with both to a previous and next letter
   (2)  Partial -Connectors, which may be joined only to a  previous letter 

The shape of a letter may also differ somewhat depending upon its position in a word and its joining or non-joining  to adjacent letter..

CONNECTORS GROUP OF LETTERS

The Connectors group of letters may have as many as four variant forms (1) Independent (2) initial (3) middle  (4) final

PARTIAL CONNECTORS GROUP OF LETTERS

The partial -connecting group  of letters may have only two forms (1)  independent and initial (2)  final