The following was saved from the old cmhpf.org website, just in case anyone was looking for it (Source: archive.org):
Doric Order
Of the three columns found in Greece, Doric columns are the simplest. They have a capital (the top, or crown) made of a circle topped by a square. The shaft (the tall part of the column) is plain and has 20 sides. There is no base in the Doric order. The Doric order is very plain, but powerful-looking in its design.
Doric, like most Greek styles, works well horizontally on buildings, that's why it was so good with the long rectangular buildings made by the Greeks. The area above the column, called the frieze [pronounced "freeze"], had simple patterns.
Above the columns are the metopes and triglyphs. The metope [pronounced "met-o-pee"] is a plain, smooth stone section between triglyphs. Sometimes the metopes had statues of heroes or gods on them. The triglyphs are a pattern of 3 vertical lines between the metopes.
There are many examples of ancient Doric buildings. Perhaps the most famous one is the Parthenon in Athens, which is probably the most famous and most studied building on Earth. Buildings built even now borrow some parts of the Doric order.
Ionic Order
Ionic shafts were taller than Doric ones. This makes the columns look slender. They also had flutes, which are lines carved into them from top to bottom.
The shafts also had a special characteristic: entasis, which is a little bulge in the columns make the columns look straight, even at a distance [because since you would see the building from eye level, the shafts would appear to get narrower as they rise, so this bulge makes up for that - so it looks straight to your eye but it really isn't !] .
The frieze is plain. The bases were large and looked like a set of stacked rings. Ionic capitals consist of a scrolls above the shaft. The Ionic style is a little more decorative than the Doric
Corinthian Order
The Corinthian order is the most decorative and is usually the one most modern people like best. Corinthian also uses entasis to make the shafts look straight.
The Corinthian capitals have flowers and leaves below a small scroll. The shaft has flutes and the base is like the Ionian.
Unlike the Doric and Ionian cornices, which are at a slant, the Corinthian roofs are flat.
There are also two other types of classical orders, the Tuscan and the Composite. The Tuscan order is very plain, with a plain shaft, a simple capital and base, and a plain frieze. The Composite order is a combination of the Ionic and Corinthian orders.