Gurukula Vyavastha translates as schooling and education system.
Selection of students and eligibility
There is scriptural guidance for determining the eligibility of a student. However the immediate and final decision on this is of the guru, as he could determine the eligibility considering changing times and situational needs along with the student's attitude and aptitude.
The selection for different vidyas will be based on aptitude and attitude of the student, along with his Varna . There could be exceptions where the guru may decide to disqualify a student in spite of his Varna or aptitude, for other reasons like the attitude/intentions of the student. And there could be occasions when a student will be accepted for a study that his varna does not otherwise qualify for.
Study - instruction
Except on specific days, instruction will typically happen after daily ritual in the early morning till afternoon.
For dwija students the curriculum includes veda and associate texts like vedangas and upangas. Besides, each class will have a different curriculum - kshatriyas will pursue things like neeti sastra, dhanurveda etc while brahmanas will continue to study the veda. Sudra students will pursue varied subjects like engineering and architecture.
Study - life in gurukula
As the name itself indicates, gurukula means extended family of the guru. Guru is the owner of the family. Students should raise food through alms and by collecting wood/eatables etc from forests. They should surrender it before the gurupatni (guru's wife) and she distributes whatever all the students collected amongst all the students after guru's share. Usually the needs like wood for household fire are also got by the students.
Guru should not take any money from the students. The guru dakshina will be paid in the end by the student, and it will be what the guru asks for.
The dharma sastras, especially the Dharma Sutras of Kalpa (like Apastamba and Baudhayana) and metrical codes like Manusmriti lay down the outline of Gurukula Vyavastha, how a guru should be, how a disciple should be, how instruction should be and so on.