Use the converMouseLocationToWorldSpace node, and use that to do a linetrace to figure out where the mouse is hovering. Use the break hitResult node to pull the hitActor, and based on that figure out what you want the player/game to do.
Bind this to an eventTick for things that happen on hover (displaying name/hp, or higligting for example)
Bind it to an inputEvent (e.g. leftMouseButton) for attacking, moving, spellcasting.
As for movement, look up tutorials on making AI movement and just adapt the code to your needs.