Gochar
Transit, or gochar, is where the planets are now, read against the positions they held at your birth. Vedic astrology usually counts transits from the Moon sign rather than the ascendant, which is why knowing your rashi matters before any of this can be read.
Which transits matter
The slow planets carry the most weight. Saturn takes about two and a half years to cross a sign and Jupiter about one, so their movements mark out periods of years. The faster planets shift the texture of days and weeks rather than the direction of anything.
Transit and dasha together
A transit acts on what the birth chart and the running dasha already allow. A favourable transit during an unrelated planetary period usually passes quietly, while the same transit during the period of a planet it touches can be quite marked. Neither is read alone.
Common questions
Should transits be read from the Moon or the ascendant?
Vedic practice reads them chiefly from the Moon sign, which is why this page counts from your rashi. Reading from the ascendant as well is common, but the Moon is the primary reference.
Which transit matters most?
Saturn's, because it is the slowest of the visible planets and stays in a sign about two and a half years. Jupiter's is next. The fast planets change the texture of days rather than the direction of anything.