Some spesifications:
In both cases, None is used if you have no idea about what you want to do, or don't care for the orders. Giving atleast a general command is needed very often, though. Targetting can be left to the AI if winning the battle is not too important.
Commanders have two sets of orders: the upper ones give them order for one turn and they can't be targeted spesifically (that means: they can attack for one turn, but cannot attack archers for one turn). The ones below these ones work as the commands given for the normal units: they affect through the rest of the battle. You can give one turn commands before the whole-battle commands, but not other way round. You can set commanders targets with these lower commands.
You can also let the AI decide spells cast or choose what you want your amges to cast by choosing "Cast a spesific spells". You will be given a list of all spells you have researched that your mage currently has paths to cast. Those spells greyed out are ones he is not able to cast at the moment, but might be when the battle occurs. If you haven't given them any item or magical gems to let them cast those spells when the battle is fought, they will choose something else.
Commanders have their own "long" orders Lasting throught the battle:
Stay behind troops and Cast spells.
Stay behind troops orders the commander to not melee, but he will shoot any weapons he has and /or cast spells if he is able to. If he would become unconscious (= fatique over 100), he might understand to stop. Mages ordered to Cast spells will do so, even if this renders them unconcious. They won't stop casting spells for any other reasons, though.
About general orders:
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Attack - use on melee troops. You propably quessed this, though.
Fire - on archers and on units that have javelins and/or throwing axes. If their ammo gets used up, even troops with Fire will attack. Archers and crossbows generally have enough ammo to not get killed when attacking though.
Hold&Attack - good for units that are meant to hold their place in, as an example, castle gate or guarding archers. They will attack after three turns, and will shoot any missiles they have while waiting.
Guard Commander - The best protection versus assasinations. Only five of the guards will be present if the assasination appen occurs, so quality is better than numbers. Numbers work too, if the assasin has no magical help or is not an Earth Elemental (Earth Attack, Conjuration 8)or anything like that. Also useful if you want to be sure your units will not advance. They won't be shooting anything, though, so not usable on archers. If your commander will go attacking, guarding troops will follow. You might find the extra control the commander provides to his units (like when you only wait for one turn before attacking) useful, but make sure that they move at the same speed!
Fire and Flee - Not really usable. Troops will fire for three turns, and then retreat from the battle. As this is considered rout, they will go to a different province altogether. It can be used if you want to make sure your archers will not fire after your infantry has closed to the melee, but causes more work.
Retreat - For those battles that you have no hopes of winning, and to use when you WANT your enemy to get that province. Those are exceptional cases, though.
About targetting orders
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- closest
Use if your soldiers are stronger than the enemy. Also useful if they don't have to do anything special. On archers if your front troops can withstand the shots.
- archers
Use on fast units, and try to kill their archers before they make too many holes on your bright new soldiers. If your enemy protects them in some way you should put the cavalry or whatever you are using to the sides of the battlefield.
-rearmost
Same as for archers, but now your units might find some defensless mages and other commanders too! On the other hand, they just as often turn back and attack the enemies' front line from behind. Archers cannot target rearmost, because that would give you easy way to get rid of enemy commanders. That was one of the most exploitable combat tricks not involving magic in Dominions 1, together with fliers flying straight to the commanders.
- cavalry
Do you have some units that are exceptionally good at giving out damage? Maybe simple Barbarians, maybe Minotaurs recruited from a random Maze? If you want to be sure that they go for those knights, use this command. Crossbowmen will kill most cavalry they shoot at if they get enough shots in, but as knights and like often have heavy armors normal bows are not as good.
- large monsters
Often same as above, but can also be used to frighten the elephants and/or mammoths. If you get them running, they will escape straight through the enemy armies! Some people like equipping their pretenders with good gear and use them to kill whole armies. With this order you can be sure that everybody tries their luck, but they surely need it against these beasts! Crossbowmen could still work, and they also good at killing big mosters. Routing elephants is easier with short bows as they will take damage multiple times, but if they don't die you still have to fight them on the next round...
- fliers
I'm not sure if there is a special use for grond forces attacking fliers. But when defending (= your side ges first), you could try to catch them before they are able to fly to your rear. Wroks exceptionally well with archers, as long as they understand to stop firing after the fliers have attacked your troops!
Whew! Too long post, I would say, but he never asked for a short answer...
Re: Questions about orders on "recruit army" for pretenders
somebody can explain the difference and importance of orders of pretender, troops.. in recruit before a battle army: attack, retreat flee ,attack on archers.. ?there is many orders very differents and i don't know which is the best to use if i don't know the organisation of the ennemy troops?
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