The hoplite first appeared around 700 BCE, during the Archaic Age of Greek history. This was the era immediately preceding the Classical Age, which is the height of civilization in Ancient Greece (and the one you all learned about in school).
Before the Hoplite...
In the Dark Age and early Archaic Age (from 1200 BCE to 700 BCE), warfare in Greece took the form of hero combat, as described by Homer in the Iliad. This was when a set number of heroes-- the best warriors, all from the aristocratic class of large land and slave owners-- from both sides would square off in a ritualistic, highly formalized fight. The winner would take all. This method of fighting was fine when men had little to lose, but as they entered the Archaic Age, they began to enjoy more prosperity, and they didn't want to stake all that they had on a single battle between a few men. Thus, we have the...
The hoplite was a heavily armed member of the infantry. He wore a bronze helmet and cuirass, and a skirt of thick leather to protect his reproductive organs. He carried a new kind of shield-- the hoplon-- which was a circular piece of wood with a bronze coating on the front. The hoplon was an innovation imported from the east, most likely from Persia. The equipment weighed about 70 pounds.
Naturally, all this armor is expensive. Naturally, each hoplite had to have an entourage of slaves to carry the armor, and to carry provisions, because this was the time when service in the army was an unpaid duty. However, there had to be a lot of hoplites in order to win battles, and the aristocratic class was too small to provide many soldiers. So, the military became a middle class operation, and a very democratic institution. All men were allowed to speak their minds, no matter what they had to say-- if they felt the need to call the leader an idiot, they had every right to do so. We see this democratization in the Iliad, which probably reflects society in the late 8th century BCE, when a lowly foot soldier castigates Agamemnon.
As the middle class took over the army, the aristocrats were forced to depend on them. Also, the army was one of the rare opportunities for upward social mobility in the Archaic Age. A skilled army man could rise through the ranks to a position where one of his daughters, with a sufficient dowry, might be married into the aristocrat class.
The hoplites fought in a formation called the phalanx. This was a tight line of men walking forward, usually eight rows deep and anywhere from a mile to a hundred feet long. The shield of the man on your right side protected your weapon arm (I don't know how lefties were incorporated into this), and your shield did the same for the man on your left, and on down the line. With your sword or spear, you would stab above or below the shields at the enemies. When one man fell, the ranks had to close to cover the gap; when advancing forward, the rows had to be close enough to push the one in front of them forward. This required a lot of training and discipline; hence, the hoplite was well respected in his community.