Quite short mission. When you jump into system, whole enemy fleet is paralyzed by a powerful EMP blast. Unfortunately, some ships begin to move very soon. Destroy them and then move all your fleet into positions around target station. Now you need to defend docked transports until boarding parties come back. There is no clever tactic, just stay near the base and destroy waves of incoming enemy vessels. If you loose any ship, immediately bring reinforcements from hyperspace. Once rebel troops come back, your task is complete.
Right after this mission Mon Mothma asks you to bring Han Solo to her. Don't do that yet, because next mission will start automatically. After that all remaining systems will become active and the empire will counterattack.
You should take some time to prepare now. Planets close to inactive systems (like Corelia, Fresia, Corulag, Alderaan, Dantooine) should be reinforced. Build defensive structures on their surface and keep some troops there. Check if Sulust, Kuat and Mon Calamari have best available space station. Once everything is set up, send Solo to Mon Mothma.