Your janma nakshatra is the star the Moon was passing through when you were born. Enter your birth details above and you will get the nakshatra and its pada, the quarter of the star your Moon fell in. It is free and needs no account.
The zodiac is divided into twenty seven nakshatras of 13 degrees 20 minutes each, an older and finer division than the twelve signs. Each has its own name, ruling planet and character, which is why two people with the same rashi can feel quite different.
It also has practical uses. Your nakshatra sets where your Vimshottari dasha begins, it feeds into guna milan when two charts are matched, and many families use it to choose a muhurat.
Every nakshatra is split into four padas of 3 degrees 20 minutes. Each pada carries its own syllable, which is the basis of the tradition of choosing a child's first letter from the birth star.
Each pada also corresponds to a sign in the navamsa, the divisional chart read closely for marriage and inner strength. So the pada is a small detail that connects your birth star to a much larger part of the chart.
They answer different questions, and you will want both. Your rashi is the broader sign used for most horoscopes, while your nakshatra is the finer detail used for dashas, matching and naming.
Yes, that is the traditional use. Each pada has a starting syllable linked to it, and families often pick a name beginning with that sound. Many also use a different everyday name, so treat it as a custom rather than a rule.
More than for your rashi, because the Moon spends only about a day in each nakshatra and a little over six hours in each pada. If you are unsure of your time, the pada is the first thing that might change.