How do I use the stairs animations

you mark how high up your character needs to be above the ground plan at the start of his animation so he doesn't go into the floor [like happens in the untested Mixamo demo] then you run the animation and mark where his feet touch on each step

in Blender [for basic testing] i would add a small plane to get a reference and go from there... if this animation was long or important i'd use Iclone but Blender is fine for quick jobs