Classic Styles are represented by the three orders of architecture: Doric, Ionic, Corinthian. Plus two additional styles which derived from them: Tuscan and Composite.
Image source: https://en.wikipedia.org/wiki/Classical_order
Classic Styles- Characteristics
The Doric order is the most recognizable style as it has simple circular capitals at the top of columns. Many of the most important Greek buildings were built using this style. Further, it is the first style of Classical Architecture and was considered a standard of beauty, elegance and strength. It is connected to the moment when monumental construction started using permanent materials, namely stones. Columns are fluted and are of sturdy, if not stocky, proportions, their shafts stand without a base on the Stygobite, which is the uppermost step of three or more steps of a platform called Crepidula. Capital consists of the Echinus and the quadrangular Abacus and carries the architrave. The latter has frieze that are composed of Triglyphs, square spaces for either painted or sculpted decoration, and metopes, marble slabs decorated in bas-relief.
The Ionic Order is primarily identified by its capital, with its rolled-up cushion-like form on either side, which creates the distinctive volutes. Vitruvius describes it as a combination of Doric and Corinthian orders.
The Ionic order incorporates a running frieze of continuous sculptural relief without the Doric triglyph and metope, yet sometimes has ornaments, such as carved figures. The Ionic column is nine times lowe than its diameter high, its shaft is eight times its lower diameter high, and it’s also marked by an entasis, or a curved tapering. A pair of volutes (scroll-shaped ornaments) decorate the capital, which is only one-third the thickness of the column.
The Corinthian order is the most elegant of the five orders. Its main characteristic is the striking capital, which is carved to create two rows of stylized acanthus leaves and four scrolls. The shaft has 24 sharp-edged flutes, while the column is 10 diameters high.
The Tuscan order is one of the two classical orders developed by the Romans. It is not an ornate style, but it is quite solid. Although it is influenced by the Doric order, it has unfluted columns and a simpler entablature with no triglyphs or guttae (literally dashes). The Romans did not consider this style to be a distinct architectural order. For example, Vitruvius did not include it in his architecture. Its classification as a formal order can be traced back to the Italian Reinassance.
The Composite order is a mixed order, as the capital is a combination of Ionic and Corinthian orders. This order is similar to the former one, except for the capital. In many versions, there is some ornament between the volutes. The column is ten diameters high, though as with all the orders these details can be changed for particular buildings.
Info source: https://en.wikipedia.org/wiki/Capital_(architecture)