Skrullos and Tarnax IV are important planets within the Skrull Empire.
Skrullos is the homeworld (Place of Origin) of the Skrull race. Tarnax IV is the Skrull Empire's Throneworld or Capital Plane of their Empire.
Full Map of Andromeda Galaxy in Marvel
Supposedly the capital was moved from Skrullos to Tarnax IV 100,000 years ago due to Tarnax being more central. (Question for educated Marvelites out there - How is Tarnax more central when both planets sit in the same star system of Drox? This seems like an error by Marvel.)
Who are the Skrulls?
Skrullos is the homeworld of the Skrulls. It was on Skrullos where the three branches of Skrulls battled in a brutal civil war. The winner of the war the shape changing Deviant Branch went on to create a massive empire in the Andromeda galaxy. The empire included 99 planets at its height with numerous member and partner races.
100 thousand years ago the capital of the empire was shifted from Skrullos to Tarnax IV 4.
Galactus the world eater struck Tarnax killing off the empire's leadership and breaking up the empire. The Skrulls would try to regain their power by conquering Earth in secret invasion but this left them even weaker.
The Skrull empire is a shell of its formerself and they are attacked again by aliens called the Builders. With the help of the Avengers, the Skrulls manage to defeat the Builders. Leading the defense of the Skrull Empire was the Super Skrull Kl'rt due to his victory he is made Emperor of Empire. The new capital planet of Skrull Empire is Tarnax II. I do not know what Star System it supposedly resides in. Hopefully, Tarnax II is not in Drox because that Star System is getting very crowded.
List of Important Skrulls Planets all in Andromeda Galaxy:
Skrullos - In Drox Star System - Home world but no longer capital
Tarnax II - Unknown Star System - Current Capital under rule of Kl'rt. Very little else is known about Tarnax II.
Tarnax IV - In Drox Star System - Longtime Capital destroyed by Galactus
Tarnax X - Unknown Star System - Where genetic changes were made for secret invasion
Kral IV -Unknown Star System (Said to be on outskirts of Skrull Empire) - Planet of Skrulls who act like 1930s humans - Mostly Mobsters and Civil rights leaders. Krallian Skrulls are said to not be trustworthy during Secret Invasion due to their affinity for human culture.
Zorogz'na - I have seen this planet called out in a starmap but I can find nothing on it. Apparently at one point after the destruction of Tarnax IV this planet is considered the symbolic home of the Skrulls. I am not sure if Zorogz'na is another name for Tarnax II which would seem to make sense.
Who are the Skrulls?
Secret Invasion Posters - WHO DO YOU TRUST
Nova Worldmind - Cosmic Races and Cosmic Map