When digging ore using the Build Gun, each attempt at mining with right click subtracts from the total resources available in that ore block. This will occasionally generate an ore, but produces a lot of rubble. This rubble can be avoided by Super Digging.
LMB will place in the world the highlighted item on the hotbar. Place a long line of blocks (Build-2-Me or Super Build) with CTRL and LMB. This will build from the target face of the block towards you until it hits your X/Y/Z coordinates. It is handy for building large platforms or walls.
MMB will select block or item you are pointing at for next placing (quickselect).