A Vedic chart is sidereal — it references the zodiac to fixed stars, not to the moving vernal equinox of the tropical zodiac. The difference between the two is the ayanāṃśa, a slowly-increasing offset (currently around 24° and growing by ~50.3 arcseconds per year). India's official standard is the Citra-Pakṣa ayanāṃśa, also called the Lahiri ayanāṃśa after N. C. Lahiri who computed it for the 1955 Indian Astronomical Ephemeris. /ayanaamsha shows our engine's current ayanāṃśa value.
Once ayanāṃśa is applied, the lagna (ascendant) is the rāśi rising at the eastern horizon at the moment of birth, for the birth location. This rāśi becomes the 1st bhāva. In the whole-sign system (the dominant Vedic approach since pre-classical times), each subsequent rāśi becomes the next bhāva — so all 30° of each sign belong to a single bhāva. This is different from Western systems like Placidus which use unequal house boundaries.
The 12 bhāvas measure 12 dimensions of life: 1st = body/self (tanu); 2nd = wealth/family-of-origin (dhana/kuṭumba); 3rd = siblings/effort (sahaja); 4th = home/mother (sukha/mātṛ); 5th = children/intellect (putra/buddhi); 6th = enemies/disease/service (ripu/roga); 7th = spouse/partnership (jāyā/kalatra); 8th = transformation/longevity (randhra/āyu); 9th = dharma/father/fortune (dharma/pitṛ); 10th = career/status (karma); 11th = gains/aspirations (lābha); 12th = losses/liberation (vyaya/mokṣa). BPHS Ch. 15 is the canonical reference.