you first have to be able to recruit a army HQ unit in the support tab, once it is finished training you need to send him into the stack of a 3 or 4* general...then if that general passes his check and can actively lead troops ( you can hover the mouse over his portrait to see weather or not he can...

I/m new to the great game and am having a real problem creating armies in campaign mode . AS armies are appointed how do you find , create or buy army HQs to go with the eligible generals . What happens to the HQs when you disband an army ?