Greetings, Commanders!
This is going to be a quick one; most of the information is already easily seen within the game. So, let’s get there!
When you are entering a dungeon, including endless, directly under where you see your heroes there is a little circle with arrows in it. Pressing here will bring up a box that shows the four current Commander Orders.

You can also see the four Commander Orders under the Commander Orders tab when you click on your avatar in the upper left corner.

But back to the box when entering a dungeon. Here you can simply select the Commander Order you wish to make available in the dungeon you are running. The default Commander Order is the Cinder domain.




I speculate here, but since the Commander Orders are represented by four of the six domains, I suspect there will eventually be two more Commander Orders in the future.
Now, picking a Commander Order isn’t enough to gain both those benefits. while the first benefit will apply immediately, for the second one, you will need to find your way to a camp inside the dungeon and select the Inspire option. The good news is that many adventure dungeons will begin at camp, allowing you to select your Commander Order at the start.

Obviously, pick the order that is applicable to the type of dungeon you are running (Adventure or Endless) and gives you buffs that benefit you.
Until next time, I will see you in Elderym, Commanders!