tl:dr you are an Aeiouian defense engineer creating a fortress remotely with less experienced foreign defensive contractors, who must eventually manage to destroy what will at that point have become very powerful enemy forces through sheer durability or eventual scratch damage, as Aeiouian military forces are not heavily armed, and not die at any point in the bargain.
The system is as follows.
As far as your base...
You have the various HP totals, which summarizes the durability of your shields, your bases, and the many things inside them. You are required to keep these high because that is the entire point of having a HP total. You have a Support total, which summarizes how willing and able external forces are to aid you in any way without notable pay, similar to KSP Prestige sort of. Keeping this high means you can randomly pull stuff out of nowhere and summon aid. Most of the time chatfight-style summons will draw from here unless they can appear from resources you've made. You have a Credits total, which summarizes how much money or other resources you have not put into anything. Resources are basically indistinguishable in the Aeiouian post-scarcity economy anyways and complex advanced contracting requiring high-level archailects to manage anyways allows you to utilize this technology without actually having it. You have a Research total, which summarizes how much SCIENCE!!! you are doing, which can be used to research new stuff for the buying. You have the Abilities bar, which points out special things you can do each turn without having to draw from chatfight summons and me having to google+react when updating. You have the various shops, where you will be able to buy things for credits.
And then you have all the units living in your base.
Battles against the enemy can be performed in any number of abstractions, but will normally be divided into a quickie system where the attack minus defense damages unit's hitpoints at a minimum of 0 damage, then regen/direct damage poisons apply, then the affected unit counterattacks if it can, etc.
The enemy runs on the same system nominally but with way more attack and usually less excessive defense ratings.
ex.
Overshield HP 100000/100000 (+500) Undershield HP 1000/1000 (+50) Base General 10000/10000 (+10) Support 495 (+1) Credits 9001 (+100) Research: 1234 (+30) No abilities recommended No special shops in town today