Rigveda. A book of hymns. Poets praise Agni, the fire, Indra, the warrior god, and Soma, the sacred drink, and ask them to come to the offering. One priest recites these hymns.
Yajurveda. A book of ritual words. It tells the priest what to say while he pours the offering, builds the altar, and carries out each step. Think of it as the spoken instructions of the ceremony.
Samaveda. A book of songs. Most of its words come from the Rigveda, but here they are set to melodies and sung. One priest chants them during the Soma rite.
Atharvaveda. A book of prayers for daily life. It has spells for healing, protection, peace in the home, and also deeper reflections. It is less tied to the public sacrifice than the other three.
A simple way to remember them: the Rigveda is the poem, the Yajurveda is the ritual script, the Samaveda is the song, and the Atharvaveda is the prayer for ordinary life.
