Its split into Layers and Parameters.
1-Layers = This is where you have all your animation tree set up, or you different layers, You use Layers, for dividing your avatar in different parts, Say, Legs, is one layer , the rest of your char is a different layer, then you can have one different animation play per layer, Walk+Aim, etc.
2-Parameters would be the conditions to drive your animations, this is where you can add the bools, So if BoolWalk is true then = play Walk Animation, Etc..
You can just play all animation using FSM it will be quiker this way and less redundant Using AnimatorCrosfade.
I hope I helped some way.