Hi Muhammad,
I assume you've read the help?
technet.microsoft.com/.../aa573189.aspx
Lets use an example of a cheese sandwich that you might buy in the supermarket. These come in a box (packaging), and consist of sandwich which is made of some bread and some cheese.
The BOM for the top-level item has two lines: Packaging and Cheese Sandwich.
The Cheese Sandwich also has a BOM with two lines: Cheese and Bread.
On the top-level item, if you set the Cheese sandwich line to 'Item', AX will want to consume cheese sandwiches that you have got in stock (either because you bought some, or you made some earlier).
On the top-level item, if you set the Cheese sandwich line to 'Phantom', AX will 'explode' through this item to the next level, and will want to consume Cheese and Bread. This is good if you make the sandwich at the same time as you put it into the packaging.
On the top-level item, if you set the Cheese sandwich line to 'Pegged supply', AX will want to consume 'Cheese sandwiches', but it will automatically create another works order to produce those 'Cheese sandwiches'.