A screw usually has a pointed end. You 'screw' a screw directly into something, for example, wood. http://www.diytrade.com/china/4/products/2448678/Chipboard_screw_Drywall_screw_Wood_screw.html You usually use a screwdriver to insert a screw. A bolt usually has a 'flat' end. They are usually used with a 'nut', and they are used to connect 2 things together (or to 'bolt' 2 things together). See the image at the link, below: http://www.simpsoncycles.co.uk/product.php/1694/loose_seat_nut_bolt Nuts and bolts are usually fitted with a spanner or a wrench.

No problem, Laurens. Feel free to ask any questions.

Thanks a lot !the description you gave me,exceed all of my expectations ! XD