So when can you bomb the population then? Do you just use a move action and instead of moving out, bomb the population?
This only happens at the end of the Combat in the hex. For "Attacking Population" section of the rules:
p20 of English PDF wrote:
After all battles have been resolved, the remaining Ships may attack the population in the hex. Each Ship may attack once with all of its Cannons (Missiles may not be used), using the normal rules to hit. Population is considered not to have any shields. Each point of damage destroys one Population Cube of your choosing. If you have the Neutron Bombs Technology, you may destroy all the Population Cubes from the hex without rolling any dice.