The word panchanga is literally "five limbs" — pancha (five) and anga (limb). A day's panchang is not a forecast. It is a measurement: five independent quantities derived from where the Sun and Moon actually are, each of which classical Jyotish reads for a different purpose. Understanding what the five are is what turns aaj ka panchang from a table of unfamiliar words into something you can act on.
Tithi — the lunar day. A tithi is the time the Moon takes to gain 12° of longitude on the Sun. Thirty of them make one lunar month: fifteen in Shukla Paksha, while the Moon waxes toward Purnima, and fifteen in Krishna Paksha, while it wanes toward Amavasya. Because the Moon's orbital speed is not constant, a tithi is not a fixed 24 hours — it can run roughly 19 to 26 hours. That is why aaj ki tithi usually ends partway through the civil day rather than at midnight, and why the panchang lists an ending time rather than a date. Almost every Hindu festival, fast and shraddha date is fixed by tithi, not by the Gregorian calendar, which is why they appear to move each year. Each tithi also carries a presiding lord, shown alongside it here.
Nakshatra — the lunar mansion. The zodiac is divided into 27 nakshatras of exactly 13°20′ each, and each nakshatra into four padas of 3°20′. The nakshatra of the day is simply the one the Moon is currently passing through; it changes roughly once every 24 hours. Nakshatra is the oldest layer of Indian astronomy — older than the twelve-sign zodiac in Indian use — and it carries most of the practical weight in Vedic astrology. It drives Vimshottari Dasha, it decides muhurta selection, and it is the basis of the Ashtakoot gun-milan used in marriage matching. Your own janma nakshatra comes from the Moon's position at birth, not from today's.
Yoga — the Sun-Moon sum. This is the limb most people misread, so it is worth being blunt: panchanga yoga is not the same thing as a chart yoga. Raj Yoga, Gaja Kesari Yoga and Kemadruma Yoga are planetary combinations in a birth chart and have nothing to do with this. Panchanga yoga is a single arithmetic quantity — the sidereal longitudes of the Sun and Moon added together, then divided into 27 segments of 13°20′. Each segment has a name, from Vishkambha through Vaidhriti. Several are traditionally treated as unfavourable for beginning new work, with Vyatipata and Vaidhriti flagged most consistently across texts. The two systems share only a Sanskrit word.
Karana — the half-tithi. A karana is half a tithi: 6° of Moon-Sun separation, so sixty karanas per lunar month. There are eleven named types. Seven are chara (movable) — Bava, Balava, Kaulava, Taitila, Gara, Vanija and Vishti — and they cycle eight times through the month to fill fifty-six slots. The remaining four are sthira (fixed) and occur once each: Kimstughna opens the month at the first half of Shukla Pratipada, and Shakuni, Chatushpada and Naga close it across Krishna Chaturdashi and Amavasya. The one worth knowing by name is Vishti, better known as Bhadra, which is widely avoided for auspicious beginnings.
Vaara — the weekday and its graha. The seven vaaras are ruled in order by Sun (Ravivara), Moon (Somavara), Mars (Mangalavara), Mercury (Budhavara), Jupiter (Guruvara), Venus (Shukravara) and Saturn (Shanivara). The ruling graha colours the whole day and is what fixes Rahu Kaal's position. One detail catches people out: in the Vedic reckoning a day runs sunrise to sunrise, not midnight to midnight. At 3 a.m. on Tuesday the panchang is still counting Monday.