This tutorial is for objects like this:

where we need to see the inside as well as the outside.

This tutorial will use a CopyPart  node to copy the triangles from the part and add the triangles back with the copied triangles inside out so that we can see the object from both sides.

Referencing a Part

To drag a part as a reference for any build node, we drag the part from the scene (not the new node bar) to the right of the the build node's  icon while holding down the Alt key:

Source and Destination Parts

Some build nodes such as CopyPart nodes can reference parts in 2 different ways, as a source and as a destination.
A source part is distinguished from a destination part by its blue dot:

When adding a part node as a source reference drag the mouse to the blue dot in the little blue square that appears before dropping the node:

When adding a part node as a destination reference drag the mouse to the blue dot in the little red square that appears before dropping the node:

Ok add the same part as a source part and as a destination part for the CopyPart node so that we see 2 references of the same part branch out of the CopyPart:

 

Setting the CopyPart's fields

Select the CopyPart node.

Check the insideOut box field

after we do this we will see our object is visible on the other side but is no longer visible on the side it was before!

To fix this check the add field box and then we will see it visible on both sides.