The concept is this:
Player clicks on screen, you convert screen coords to world coords (vec_for_screen) and use the result and result + z position for depth and trace to get ground coordinates.
I guess you can move your entity from that point yourself

I'd also suggest you browse for the tile tutorial, because making a 3d point and click without tiles can be messy and buggy. If you have tiles it becomes 10 times simpler, even if the tiles are small.