This building block is a slope corner with its cusp (pointed end) pointing and fitting to one corner of an adjacent cubic block. It is not pyramid-shaped.
Bedrock Slope Outer Corners were implemented during the launch update in May 2017, together with many other Roof and Slope corner blocks.
Cutting blocks in a Processor does not require any crafting recipe.
The slope corner blocks can be rotated by pressing and holding R (as the default key) and moving the mouse while holding the left mouse button. The chosen rotation angle can be "locked" too by simply typing "r" while looking at a rotated block or item, so next all items of the same stack will be placed facing the same direction.