What a saṃskāra is
The word comes from sam-kṛ, “to put together well, to refine”. Just as gold is purified in fire, tradition sees these rites as gently shaping a person's character and welcoming them into a new stage of life.
Most saṃskāras are gṛhya rites, described in the Gṛhya Sūtras, and many include a small homa, Vedic mantras and the blessings of elders. Their social side matters as much as the ritual: the family gathers, the child is named before everyone, the couple make their promises in public.