Civil flights are mainly used for transportation of cargo, scouting, solar power generation, recycling etc,. There are many other uses beyond what you see. For example Recyclers, the more you have the more you can capture recycling materials. More can be know in individual sections.
Combat flights are mainly used for exploring attacking. There are many types of combat ships. These ships can be unlocked by upgrading "shipyard" as well as certain researches in "research center". Shipyards have different attributes on different planets but research labs share same attributes except their levels. More can be know in individual sections.
Defences are a must for your planets, and these are differentiated into four main categories. Among these all three have attacking abilty while the other one is purely for defence-"Shiels". Each of these categories have certain level of upgrades. More can be know in individual sections.
This is a special edition for dwarf solar system. Here you can analyze the amount of combat flights you need to attack dwarf solar system can be analyzed based on your different technology research levels. Hopefully this is one of the best help for avoiding losses. More can be know in individual sections.