In general, inflorescence of orchid plants bear multiple flowers. Many species produce multiple inflorescences, thus with a large number of flowers. More the flowers, more the chances of getting pollinated and seed production.
However, there are many species that produce a solitary flower. In these cases, the plants have evolved to produce large and showy flowers or flowers with odour to attract pollinators.
Flower characteristics are mainly to attract pollinators. Important and noticeable features include colouration of sepals and petals, position of the lip and odour (only in a few species).
However, many orchid species have evolved to great extent in having hidden or unnoticeable features (to human eyes) like colour patterns/spots on its anther cap and base of the lip to allure the pollinators deep inside the flowers to make effective pollination.
In resupinate orchid flowers, when buds are formed they are upside down – meaning the lip and spur (if present) are on top side of the bud. As the buds develop, the pedicel twists either clockwise or anti-clockwise to invert the bud, thus arranging the lip and spur to the bottom side of the flower. This arrangement helps visiting pollinators.
(Note: Pics of spurred buds are used to make the lesson more easier).