The standard modern retreat has a fixed shape, and describing it is more informative than describing the theory behind it.
Students arrive, hand in phones, books and writing materials, and undertake to remain for the whole period. Men and women are housed and seated separately. Noble silence is kept throughout: no speaking, no gestures, no eye contact, with questions to a teacher permitted at set times. The day begins around four in the morning and ends around nine at night, with roughly ten hours of formal sitting broken by meals and rest. Food is vegetarian, with breakfast and a midday meal only and fruit or tea in the evening. Five precepts are undertaken for the duration, including celibacy and abstention from intoxicants.
In the Goenka form the first three days are given entirely to observing the breath at the nostrils, which builds the concentration everything else depends on. From the fourth day attention is moved systematically through the body, part by part, observing sensation without reacting to it, on the principle that craving and aversion attach to sensation and can be interrupted at that point. Several sittings each day are designated as ones in which the student does not move at all, and those are where most people meet the difficulty.
Courses are free. There is no charge for teaching, food or accommodation, and donations are accepted only from those who have completed a course, on the reasoning that each student is paid for by the last. That arrangement is unusual enough to state plainly, because it removes the commercial incentives shaping most of the modern meditation landscape.