If a rashi says what kind of energy is present, a bhava says which part of life it lands in. The twelve bhavas are counted from the ascendant and cover, in order: body, wealth, siblings, home, children, conflict, partnership, transformation, fortune, career, gains, and loss or release.
How the twelve are cut from the sky is a real methodological fork. Most Indian practice uses whole-sign bhavas: the rising sign is the entire first bhava, the next sign is the entire second, and so on. The graha positions and the bhava boundaries then coincide, which makes charts easy to read and easy to check. Several other systems — Sripati in India, Placidus in the West — divide by unequal arcs instead, so a graha can sit in one sign but a different house. Two competent astrologers using different house systems will disagree about which house a graha occupies, and neither is calculating wrongly.
Bhavas are also grouped. The kendras (1, 4, 7, 10) are the load-bearing positions; the trikonas (1, 5, 9) are the fortunate ones; the dusthanas (6, 8, 12) are the difficult ones. A graha ruling both a kendra and a trikona is the raw material of a raja yoga.
One caution worth carrying: the classical labels for the dusthanas are severe, and a chart with grahas there is not a chart with a bad life in it. The sixth is also service and medicine, the eighth research and inheritance, the twelfth seclusion and release.