The celibate-student must perform samidadhana every day, beg for his food and take no salt. If he is a Brahmin he must keep a staff(danda) or palasa, if he is a ksatriya a staff of asvattha. The vaisya brahmacarin has a staff of udumbara. The staff helps the student to retain his learning. It is similar to the lightening conductor or the aerial and is scientifically valid as to "fix" these hymns. That is why it should be kept-to safeguard the treasure called the Vedas that the student has acquired. The brahmacarin must wear the skin of the black antelope(krsnajina) and must not wear any upper cloth. There are rules the electrician has to observe for his safety: he must stand on a rubber plank or wear rubber gloves during work. Similarly there are rules prescribed by our great men of the past to protect the Atmic electricity, the Atmic energy.
Today we perform upakarma as a one-day ceremony without keeping up the study of the Vedas. We do not go through the utsarjana at all. For our failure to do it we mutter a mantra in expiation, the mantra called "Kamokarsit"which says, " I did not sin. Kama(desire) did it. Anger did it. . . " There is no need to repeat this mantra if we perform the utsarjana.
Brahmacarya implies adherence to a number of rules with regard to food, the performance of rites and the observance of vratas. If a brahmacarin makes any mistake in chanting the Vedas, in matter of tone or enunciation, he must do penance for the same on upakarma day. On this occasion he eats no more than a few sesame seeds; otherwise he fasts the whole day; and on the following day he offers 1,008 sticks of the palasa in the sacred fire chanting the Gayatri. He should do this every year. Nowadays brahmacarins perform this rite only on the day following the first upakarma following the upanayana. Actually this a rite all Brahmins are expected to perform, though we find today householders doing only Gayatri-japa. When you merely mutter the mantra you feel sleepy and you may go wrong in the japa. But such will not be the case if you also perform a homa as you chant the Gayatri. Sticks offered in the fire must be those of palasa, if not of the asvattha; darbha grass may be used if the other two are not available.
At mealtime the student can have his fill. The only restriction is that he must not give free rein to his appetite. He must beg for his food for such a practice makes him humble. The sastras do not require him to fast. The student must be nourished properly during his growing years. But he must, at the same time, learn to develop sattvic qualities and there must be nothing rude or rough about him. It is by serving his guru that these qualities are inculcated in him.
During the twelve years in the gurukula the student must learn his recension of the Vedas and also the caturdasa-vidya. On completion of his stay in the gurukula he performs the samavartana, returns home and marries.
For a general background, please see here