Fontographer 5

Creating arabic fonts using font lab - (Ligatures) - help needed

Dears Typophilers,
I'm new in the typography design.
I did an arabic font with Fontographer 5 but I didn't finish because I need some help.

I need to know how I can create Open type standard ligatures feature with Fontographer 5, font lab or Volt.

or I need to know how I can create ligatures feature.. when I type some letters together the glyph replaces.. for example AL-JALALAH WORD (ALLAH), in some fonts if you type LAM LAM HAA it will have specific shape.

any tutorials, lessons or hints will be very helpful.