The nine grahas are the working vocabulary of Jyotish. Everything else in a chart — signs, houses, aspects, periods — describes where and when a graha acts. Nothing acts except a graha.
The list is not the list of planets, and the difference matters. "Graha" comes from the root grah, to seize or grasp, and it names something that takes hold of a person's circumstances. On that definition the Sun and the Moon belong — they are the two most conspicuous things in the sky — and so do Rahu and Ketu, which are not objects at all but the two points where the Moon's orbit crosses the ecliptic. Uranus, Neptune and Pluto were discovered in 1781, 1846 and 1930 and are absent from the classical texts. Some modern Indian astrologers use them; most do not, and a Jyotish reading that leaves them out is not incomplete by its own standards.
Seven of the nine own signs, are exalted in one sign and debilitated in the sign opposite. Rahu and Ketu own nothing in most schools, which is part of why they are read as amplifiers of whatever they sit with rather than as agents in their own right.
The practical consequence for a beginner: learn the nine before learning anything else. A reading is a sentence about grahas, and the rest of the grammar is meaningless without the nouns.