How the nakshatras work
The zodiac’s 360 degrees divide into 27 nakshatras of 13°20′ each, from Ashwini at 0° Mesha to Revati, which ends at 30° Meena. Each is divided into four padas of 3°20′, so the 108 padas map exactly onto the 12 signs and onto the 108 Navamsa divisions.
The nine planets rule the nakshatras in a repeating order: Ketu, Venus, Sun, Moon, Mars, Rahu, Jupiter, Saturn and Mercury. That order is the Vimshottari dasha sequence, which is why your birth star decides the planetary period you were born into.