Use the Selection Tool to select two points to create a cuboid within those points.
When creating a Cuboid you get up to 26 anchor points which can be used to resize the cuboid. Simple click on the anchor points with your Selection Tool.
Selecting a Corner Anchor Point makes a free resize in all dimensions possible.
Selecting a Edge Anchor Point will lock one dimension to make a more precise resizing possible.
Selecting a Surface Anchor Point will lock two dimensions. Which means that yo can only move it in one direction
By using the Chat Buttons that appear after creating the cuboid you can move the whole cuboid relative to you by one block per click.
To remove the cuboid you simply have to hold anything but a Selection Tool in your hands.