Let us start with the easiest of all.
747 - has that bump on top which is the upper deck!!
727 - has a third engine at the base of the tail plane
737 - usually quite small in length
757 - longs quite long for the size of its fuselage - if you look at one from the front, the diameter of the fuselage looks v.small
767 - length of 757, but with a noticably bigger diameter fuselage
777 - often described as a pregnant 767 - the area of fuselage under the wings longs like it is bulging, also its 2 engines are huge in diameter.
717 - two engines at rear of fuselage, rear wings are at the top of the tail plane, not the base.
go to:
www.!!!!!!!!!!!!!!
and have a look at pictures of each, you will soon spot obvious differences.
i.e 747 has 3/4 windows on upper deck
747-200 has a full set of windows
747-300 extended upper deck with set of windows then a door then another set of windows
747-400 same as 747-300 but has winglets.