Ground units are always AI run, but you can give them goals to achieve like general scouting, getting to a destination, patrolling or taking over a sector;
in addition, conditions can be setup such as what to do when encountering an enemy or if health drops too low.
There are many more things not listed here and these make up your Rules of Engagement which is synonymous for how you want your troop AI to behave.
You are in essence a general sitting in safety giving periodic plans to your troops and they carry out your strategies to the best of their ability.
Every 5 minutes is a full cycle in which all units on the planet regain and expend all their AP whether by carrying out actions or just passing when their turn comes around.
Small units like infantry in hidable-capable terrain such as forests can pass their turn, thus burning up 1 AP, to prepare ambushes for units moving into adjacent hexes.
Units with higher AP get more actions during a cycle but also generally cost more AP to move to another hex; this allows us to make high AP units effectively have a faster "reaction time" while not necessarily allowing it to move further than units with lower AP.
Sectors only become disrupted if troops are in a sector and actively occupying it.
Occupation of every sector associated with the planet is required to overthrow the current ruler.
Some planets may have multiple layers and have sectors in each, such as gas giants with a gas layer and either a solid or "buoyant" layer.
Layers may require advanced technology to access and build on.
Without adequate technological advancement it may be impossible for a player to conquer another players planet.
Allied troops can assist in defense but fielding troops is expensive, more so when deployed on allied planets, and failure to pay your troops may result in them deserting or defecting so having more troops that you personally need does have ramifications.
Ground troops are carried on ships but for the most part they cannot be deployed unless the fleet has full control of space around a planet.
Dropping troops on a planet requires 60 seconds of not taking any action including movement and not taking any damage, even AoE based damage.
Beginning the drop troop procedure will alert everyone to which unit is attempting to do it and upon completion, either by successfully dropping troops or by being canceled by the player or opposing players actions will put it on a large cooldown.
Planet defense platforms cannot be permanently defeated from space and will actively prevent troops from dropping.
You cannot bombard a planet, all occupation efforts must come form troops manually subduing sectors over many cycles.
The larger the populations are in the sectors the longer occupation takes and the more likely NPC guerrilla units will spawn to contest occupation.