Army Formation Presets are a useful concept to allow you to prespecify a configuration of your marches, so that it requires less clicks to for example attack a monster or an enemy castle.
01/10/2017 - www.youtube.com - www.gamesguideinfo.com
Explanation of the Army Formation concept in King of Avalon. How it can be used to deploy troops faster.
You can specify Army Formations in the Parade Ground. The Parade Ground is located just outside the City Wall to the southwest of the resource buildings. Here there are three flags at the right bottom. When you click on one of the Green flags you go to a similar screen as if you would compose a march, with as a difference you have a Save button instead of a button to initiate the March. Do not forget to include your Dragon if you would normally do so, otherwise you are also missing out on any applicable Dragon March Size increase.
Once you specified one or more Army Formations you can use them via the same flag shortcuts (added to the window that allows you to select troop composition after selecting a target to march on) when you give troops orders to march.
All three of the Army Formation Slot need to be unlocked. You can increase the number of slots by one when your Stronghold reaches level 10, by one once you reach VIP 6 (and have VIP active, I am not completely sure, in the Parade Ground it claims it is VIP 5, but when I look at the VIP boosts it is only added at VIP 6. I am already at VIP 7, so can't check this anymore), and by one by researching a new Army Formations project in the Combat Research Tree (just after Monster March Speed II, requires University lvl 17) to a maximum of 3.
For any of your typical activities you might use these Army Formations. For example attacking monsters works best (in my experience) without Siege Units, so you can specify an Army Formation without Siege Units for attacking monsters, with for example an equal ratio of the other three troops.
For attacking other castles you might have figured out what works best for you, this can depend on your specific boosts, and for this you might want to include an Army Formation that is more heavy on siege.
Army Formation Presets are a nice addition. They make it easier and less likely you make mistakes once you have figured out which formations work best for you.