What is a nakshatra?
A nakshatra is one of twenty-seven lunar mansions in Vedic astrology. People often look it up as a birth star, or janma nakshatra, because they want the name of the star the Moon was in when they were born. The Moon moves about thirteen degrees each day, so it usually changes nakshatra within a day. Your Moon nakshatra is the mansion the Moon occupied at the moment you were born. Each nakshatra has its own planetary lord and its own character. Each is also divided into four smaller parts, called padas. The twenty-seven nakshatras are not the same as one another. Ashwini, Rohini, Magha, and Revati, for example, each describe a different quality of mind and path. A magazine Moon sign names a whole rashi, which covers thirty degrees of the sky. A nakshatra is a smaller part of that same sky, so it tells you more precisely where the Moon sat at birth.
Why Vedic timing begins with the nakshatra
Vimshottari dasha is the timing system used most often in a janam kundli. It is counted from the Moon's nakshatra. That is why a Vedic reading names the birth star, while a sun-sign column usually does not. The nakshatra is used for timing, not only as a label. It tells you which graha begins the life, and how far through that first mahadasha you already were at birth. Two people with the same Moon sign can have different nakshatras, and therefore different dasha periods. That is a common reason two people with the same tropical Cancer sign can feel quite different, and why a Vedic Moon still needs the nakshatra named.
Nakshatra, mind, and matching
The Moon nakshatra describes how a life feels from the inside: habit, sleep, mother, and the usual mood of the mind. In kundli matching, gun milan is scored from the two Moon nakshatras. Gana, yoni, nadi, and the rest of the ashtakoot list come from those mansions, not from the Sun sign. A reading about love, family, or the mind will come back to this star. It will still need the house the Moon occupies from the lagna, and the grahas that touch it. The birth star is an important part of the chart, but it is not the whole kundli.
You do not pick a nakshatra from a list
An online list of lucky nakshatras cannot tell you yours. Your janma nakshatra is calculated from date, time, and place of birth, in the sidereal zodiac. If you only know a tropical Moon, the nakshatra may differ, for the same reason the Vedic Sun often differs. VedicAstrology.com calculates the Moon and its nakshatra from the birth details you give, then you ask. The reply stays with that birth star, that pada, that dasha, and the rest of the janam kundli. You do not need to recite all twenty-seven names. You need an accurate birth time, and a question from the life you are living.

