Ballet class usually begins at the barre, a long rail that dancers use to help balance while working on their technique. The first exercise may be either a warm up or pliés. The warm up is an exercise that warms up most of the body a little bit. It usually consists of demi pliés, tendues, and ports de bras. The plié action is the bending of the knees, in one of the turned out ballet positions, usually first position in the warm up, (first position has the feet turned out side by side so the heels are touching), the tendue action is pointing and stretching, (the English translation for tendue), of the feet, usually accompanied by straightening the leg, and the ports de bras is moving the arms and the body with the arms through a series of back bends to warm up the back and arms.
If no warm up exercise is done, then the class will start with pliés. In a plié exercise, beginner dancers will only do demi pliés in first position. A demi plié is where the knees bend about half way, so that the heels do not leave the floor. As a dancer progresses, he or she will incorporate both demi and grand, (complete bending of the knees), pliés in four of the five positions. Only four positions are used because third is considered a "training position" for fifth and only one of the two will be used. Eventually the plié exercise will include other elements as well such as ports de bras.
The second exercise is usually tendues. This is the stretching and pointing of the foot. The tendue exercise helps develop the dancer's point so it looks nice and strengthens the dancer's foot and leg. There may be two tendue exercises, the first a slower one to work on the technique of the tendue, (moving each part of the foot separately, going "through" the foot), and the second, a faster, more complicated one to work the dancer's brain as well.
As the barre session progresses, the dancers will do many more exercises, each designed with a specific purpose, to work on a certain movement or to strengthen a certain muscle. Some of the exercises are dégagé, which is like tendue but usually faster and the foot comes off the floor, frappé, which involves "striking" the floor with the foot. Then ronds de jambe à terre, moving the leg around in a semicircle on the floor, warming up the hips, fondue which involves bending and straightening both legs, with the working leg, (the one not holding the dancer up), quite often held in the air, and adage, which will definitely involve holding the working leg in the air for a while thus strengthening the muscles of the stomach, back, and legs. Finally, the barre finishes with grand battements, or "big beats;" these are the big kicks that dancers do, and except for possibly a stretch and some drills the dancers are finished barre.